I think its just the non-exit nodes that are needed as long as the traffic stays inside the tor network, I dont think an exit node gets involved at all, but I’m not 100% sure

I think staying inside the tor network helps reduce the load on exit nodes, which helps all tor users who need to access the clearnet. I think there is even a HTTP header that can be put on the clearnet site that will put a button on the tor browser that tells users that there is a onion available.