Currently libbe mangle boot environments mountpoints while mounting them.

For example: 
$ sudo beadm mount oi-hipster-2016-08-23 /mnt

$ zfs list |grep oi-hipster-2016-08-23

rpool/ROOT/oi-hipster-2016-08-23  27.7M  40.8G  38.9G  /mnt
Now if we reboot system in such state, without unmounting boot environment, on fresh boot mountpoint will be incorrect. When BE has one filesystem, it's not critical. But when BE has, for example, the following structure: 

rpool/ROOT/hipster-2016-10-29              30.1M  3.90G  7.39G  /

rpool/ROOT/hipster-2016-10-29/var          7.33M  3.90G  1.39G  /var
on boot rpool/ROOT/hipster-2016-10-29/var will have incorrect mountpoint, set to /mnt/var . fs-minimal will refuse to mount it, and system will not boot.
One of the methods to solve it is to avoid setting zfs mountpoints while mounting boot environments. To do it we use zfs_mount-like function mount_zfs() in libbe, which uses mount(2) to mount ZFS filesystems.

# beadm list 
BE                         Active Mountpoint Space Policy Created
hipster-2016-10-29         -      -          30.1M static 2016-11-19 13:15
hispter-2016-12-08         -      -          30.5M static 2016-12-08 22:26
hipster-2016-12-17-be-test NR     /          18.3G static 2016-12-17 14:02
# beadm mount hipster-2016-10-29 /mnt
Mounted successfully on: '/mnt'
# beadm list
BE                         Active Mountpoint Space Policy Created
hipster-2016-10-29         -      /mnt       30.1M static 2016-11-19 13:15
hispter-2016-12-08         -      -          30.5M static 2016-12-08 22:26
hipster-2016-12-17-be-test NR     /          18.3G static 2016-12-17 14:02
# zfs list |grep hipster-2016-10-29
rpool/ROOT/hipster-2016-10-29              30.1M  3.99G  7.39G  /
rpool/ROOT/hipster-2016-10-29/var          7.33M  3.99G  1.39G  /var
# beadm umount /mnt
Unmounted successfully
# beadm mount hipster-2016-10-29 /mnt
Mounted successfully on: '/mnt'
# beadm umount hipster-2016-10-29
Unmounted successfully
# pkg uninstall -v --require-new-be --be-name hipster-2016-12-17-be-test-1 media/wildmidi
...
# beadm list 
BE                           Active Mountpoint Space Policy Created
hipster-2016-10-29           -      -          30.1M static 2016-11-19 13:15
hispter-2016-12-08           -      -          30.5M static 2016-12-08 22:26
hipster-2016-12-17-be-test   N      /          112K  static 2016-12-17 14:02
hipster-2016-12-17-be-test-1 R      -          18.6G static 2016-12-17 22:46
# beadm mount hipster-2016-12-17-be-test-1 /mnt
# zfs list |grep hipster-2016-12-17-be-test-1
rpool/ROOT/hipster-2016-12-17-be-test-1      13.6G  3.81G  7.50G  /
rpool/ROOT/hipster-2016-12-17-be-test-1/var  3.44G  3.81G   733M  /var
# df
Filesystem                                  1K-blocks    Used Available Use% Mounted on
rpool/ROOT/hipster-2016-12-17-be-test        11859016 7866134   3992882  67% /
swap                                          4361200    1204   4359996   1% /etc/svc/volatile
rpool/ROOT/hipster-2016-12-17-be-test/var     4743858  750976   3992882  16% /var
swap                                          4360004       8   4359996   1% /tmp
swap                                          4360056      60   4359996   1% /var/run
rpool/export                                  3992907      25   3992882   1% /export
rpool/export/home                             4035270   42388   3992882   2% /export/home
/export/home/leoric                           4231317  238435   3992882   6% /home/leoric
rpool                                         3992921      39   3992882   1% /rpool
rpool/zones                                   3992907      25   3992882   1% /zones
rpool/ROOT/hipster-2016-12-17-be-test-1      11858253 7865371   3992882  67% /mnt
rpool/ROOT/hipster-2016-12-17-be-test-1/var   4743798  750916   3992882  16% /mnt/var
# init 6 ###### After this system would not go up clean earlier

##### After system boots to new BE, checking bootadm

# bootadm install-bootloader -v
be_do_installboot: device c2t0d0s0
  Command: "/usr/sbin/installboot  //boot/pmbr //boot/gptzfsboot /dev/rdsk/c2t0d0s0"
  Errors:
bootblock version installed on /dev/rdsk/c2t0d0s0 is more recent or identical
Use -F to override or install without the -u option
# bootadm list-menu 
the location for the active menu is: /rpool/boot/menu.lst
Index  Default  Dataset                                  Menu 
0      -        rpool/ROOT/hipster-2016-10-29            hipster-2016-10-29
1      -        rpool/ROOT/hispter-2016-12-08            hispter-2016-12-08
2      -        rpool/ROOT/hipster-2016-12-17-be-test    hipster-2016-12-17-be-test
3      *        rpool/ROOT/hipster-2016-12-17-be-test-1  hipster-2016-12-17-be-test-1

I created zone and checked that beadm behaves as expected with zone's datasets.
# beadm create test 
Created successfully
# beadm mount test /mnt
Mounted successfully on: '/mnt'
# df  |grep /mnt
rpool/ROOT/test                              12688466 7865467   4822999  62% /mnt
rpool/ROOT/test/var                           5872819 1049820   4822999  18% /mnt/var
rpool/zones/test/ROOT/zbe-1                   5919408 1096409   4822999  19% /mnt/zones/test/root
# zfs list |grep zones
rpool/zones                                  1.05G  4.60G    26K  /zones
rpool/zones/test                             1.05G  4.60G    31K  /zones/test
rpool/zones/test/ROOT                        1.05G  4.60G    29K  legacy
rpool/zones/test/ROOT/zbe                    1.05G  4.60G  1.05G  legacy
rpool/zones/test/ROOT/zbe-1                   134K  4.60G  1.05G  legacy
# beadm umount /mnt
Unmounted successfully
# zlogin test
# beadm list
BE    Active Mountpoint Space Policy Created
zbe   NR     /          1.05G static 2016-12-17 21:46
zbe-1 xb     -          134K  static 2016-12-17 22:05
# beadm mount zbe-1 /mnt
Mounted successfully on: '/mnt'
# df  |grep zbe-1
/mnt               (rpool/zones/test/ROOT/zbe-1): 9628835 blocks  9628835 files
# zfs list 
NAME                          USED  AVAIL  REFER  MOUNTPOINT
rpool                        18.5G  4.59G  38.5K  /rpool
rpool/zones                  1.05G  4.59G    26K  /zones
rpool/zones/test             1.05G  4.59G    31K  /zones/test
rpool/zones/test/ROOT        1.05G  4.59G    29K  legacy
rpool/zones/test/ROOT/zbe    1.05G  4.59G  1.05G  legacy
rpool/zones/test/ROOT/zbe-1   134K  4.59G  1.05G  legacy
# beadm umount /mnt
Unmounted successfully
# df  |grep zbe-1        ###Shows nothing