Yes, Owncast [0] is another example of a media app that is in the process of adding ActivityPub protocol support [1] and become part of the Fediverse. I hope they'll be largely compatible in the way they implemented their federation support.
Peertube uses very simple and straightforward ActivityStreams (JSON) properties so it's very unlikely anyone is going to make something incompatible.
However, i don't think every property is standardized yet, so having another implementation will be useful to specify everything for future implementations.
[0] https://owncast.online/
[1] https://github.com/owncast/owncast/tree/gek/activity-pub-1