I'm new to Ubiquiti routers, but I had no problem dividing the /60 I got from my ISP and assign /64s to VLANs.

You might be interested in https://www.youtube.com/watch?v=KZpJvpm1Ris (title: Does UniFi FINALLY support IPv6 Properly? State of IPv6 with Unifi Network v9). The video is about a year old, but from the looks it's not terribly outdated.