Interact with the player and see if they respond. After a minute or two pm them to see if they are around or just happened to miss your chat lines. If there's no response, just move on.
People will be OOC in Regalia at times, and that's just something we have to make peace with. It's not that bad unless you are ignored by everyone around you, which from my knowledge never happens since most of us are pretty chill about interactions.
Spidermen and Batmen will spawn at times. They just joined the server so are probably just going through the 5 minute test to see if they like what they see. I don't think it's a bad thing that they are around, and I've talked to a few of them at times much to their relief, as some of them really were interested but just needed that extra hand.
As for the last bit, not every roleplay should have spectators in it. While public areas are fair game, it walks into metagaming when you are listening in to a private conversation. If you want to hear the roleplay, move over towards it. Who knows, you may end up thrown into the scenario, which is a lot better for learning how to rp than watching others do it. You only get better by practicing.
I'm mostly against this for the survival side of things. Sure players are hidden in Regalia, but making it exclusive to one map out of a few seems like a lot of work for limited gains.