Do my scenes and overlays come over?

Yes. Scenes, sources and their order come over with the import; check any browser sources that needed a Streamlabs login.

Can one camera be in several scenes?

Yes. In OBS, add the same camera source to each scene (Add Existing), so it opens once.

Help · Set up

How to stream and feed Chatroulette from one OBS, without Streamlabs

One OBS can do both jobs: stream whatever scene you switch to, and send the stranger on Umingle or Chatroulette one fixed scene through the Virtual Camera. Since OBS 30 the Virtual Camera can be locked to a scene, so switching scenes on stream never changes what the stranger sees. Import your Streamlabs scenes into OBS, lock the Virtual Camera to your camera scene, and stream from OBS through atme. Streamlabs is no longer needed.

OBS → Scene Collection → Import → Streamlabs, then pick the collection it finds
OBS → the gear next to Start Virtual Camera → Output Type: Scene → your camera scene → OK
Start Virtual Camera, and pick "OBS Virtual Camera" as the camera on Umingle or Chatroulette
atme Settings → Multistream → Stream from: OBS
atme Settings → OBS → copy the studio link and add it in OBS: Docks → Custom Browser Docks
Press Go live in atme. Close Streamlabs.

Why it used to take two apps

The Virtual Camera used to send whatever scene was on air, so every scene switch for viewers also changed what the stranger saw. Locking it to one scene (OBS 30 and later) ends that.

Going back

Importing leaves Streamlabs as it was. Switch atme back with Settings → Multistream → Stream from: Streamlabs or another app.

Questions

Do my scenes and overlays come over?: Yes. Scenes, sources and their order come over with the import; check any browser sources that needed a Streamlabs login.
Can one camera be in several scenes?: Yes. In OBS, add the same camera source to each scene (Add Existing), so it opens once.