There are various groups, pages and posts related to Mastodon, Diaspora and the Fediverse. I don't think there is an algorithm proactively banning people for promoting it.
I don't think so either, although I wouldn't reject the possibility that those topics have some weight in the algorithm, whether intentionally or thanks to statistics. I do reject the absurd and dismissive "do people seriously believe Sheryl Sandberg is sitting somewhere banning..." mischaracterization of the argument.