Latest OBS fully works on latest Catalina 10.15 Beta (19A546d) [video capture on integrated camera, audio output capture, integrated mic capture, etc..] if you start it from the command line:
On terminal, just run:
/Applications/OBS.app/Contents/MacOS/OBS
You will be asked to give Camera and Mic permissions after starting (the first time only), no crashes while configuring camera, and no crashes at all. Fully working.