I don't recall their latest hardware is supported, but why would you want that anyway if you're not looking to go all in on their controller stack?
That said, I have some concerns that the OpenWRT AP firmware is not as optimized as the Unifi firmware is for that specific hardware. Mostly for wireless performance, but I also don’t want to hit some weird CPU bottleneck.
Have you looked at Mikrotik? They offer a more traditional autonomous OS w/o controllers and both a nice CLI and a powerful GUI tool.