From zfs(8):

     casesensitivity=sensitive | insensitive | mixed
           The casesensitivity property is currently not supported on FreeBSD.

On 10.0-RELEASE-p7 running GENERIC:

# zfs create -o casesensitivity=insensitive -o mountpoint=/tmp/i tank/i
# echo a >> /tmp/i/F
# echo b >> /tmp/i/f
# ls /tmp/i
F
# cat /tmp/i/F
a
b
# zfs get casesensitivity tank/i
NAME    PROPERTY         VALUE        SOURCE
tank/i  casesensitivity  insensitive  -

The man page should be updated to reflect that this feature works.