Good WebRTC platform provider for use with Meteor?

WebRTC always needs a back-end, for the initial handshake to setup the connection (ICE protocol). When everything is set-up, communication happens directly on a P2P basis.

However, you would also need to implement a media server if you want to support conferences with many participants. It is possible to do it without, but that causes a lot of network traffic and load on the devices.

Yes. Am I correct in thinking that a service such as Temasys can provide that back end? In development I added Temasys code to the front-end only and was able to set up a working audio-video call between two computers.

Yes, sure. That’s what these services are actually for.