People are misinterpreting me, thinking I mean that it's not even possible to intermingle equipment. That is not the case.

The specific issue I ran into was that I had a non-ubuiqiti router and AP on my network, and there was absolutely no way to set firewall rules on the Ubiquiti gateway for any clients connected through the non-ubiquiti equipment. This should obviously not be a problem. The gateway provided those clients IP addresses through DHCP and they are in its ARP table, so it should be supported.