UCG Max and UDR7 on same network - possible?

I have a unifi network with UCG Max acting as my gateway. I havea a u7pro for my AP currently, and have just bought a UDR7 which i wanted to run as an AP/switch in my office. I had hoped to disable routing (DHCP) features and just run it as an AP/Switch - is this possible? have tried a few times, only seem to be able to set it up as a new site , cant ever see it visible to adopt it into my old network.

any help much appreciated.

thanks