I suggest sshing to one of your Unifi APs and verifying. My APs are running firmware version bz.6.5.28 released 3 months ago. It is based upon OpenWRT 17.01.6 according to the /etc/openwrt_release file on the AP.
Edited: Added newlines for file content. I originally posted this from mobile in a hurry. Copy/pasting from the ssh session on my phone resulted in newlines being lost.
Below are the complete contents of the file:
DISTRIB_ID='LEDE'
DISTRIB_RELEASE='17.01.6'
DISTRIB_REVISION='r3979-2252731af4'
DISTRIB_CODENAME='reboot'
DISTRIB_TARGET='ar71xx/ubnt'
DISTRIB_ARCH='mips_24kc'
DISTRIB_DESCRIPTION='LEDE Reboot 17.01.6 r3979-2252731af4'
DISTRIB_TAINTS='no-all mklibs busybox'
Edited: Added newlines for file content. I originally posted this from mobile in a hurry. Copy/pasting from the ssh session on my phone resulted in newlines being lost.