Please add to your /etc/devfs.rules

[devfsrules_unhide_all=65535]
add unhide

Please add to your /etc/rc.conf:

jailup_enable="YES"
devfs_rulesets="${devfs_rulesets} /usr/local/etc/jailup/rules"
devfs_system_ruleset="devfsrules_unhide_all"

and run

/etc/rc.d/devfs start

after.
Devfs system ruleset can be another, just keep variable
devfs_system_ruleset not empty and assign to it proper value.