I don’t have a Dream Machine nor a 192.168.0.0/16 network but my access point receives an IP via DHCP from a non-Ubiquiti router just fine. In fact, the controller running in Docker doesn’t even come up itself after a power failure so I’m really lost on what you’re talking about here.
I really love what Ubiquiti is trying to do, but I understand where you’re coming from. I ditched the EdgeRouter X because I just couldn’t do anything really advanced with it.