You don't need separate accounts to interact with different kinds of Fediverse servers.

For example, if you have a Mastodon account you can follow PeerTube accounts such as @theatticdwellers or @alliterative and their videos will appear in your Mastodon timeline as if they were Mastodon posts.

If you reply to a PeerTube video within Mastodon, the reply will also appear as a comment below that video on PeerTube. (And comments made on PeerTube will appear as replies on Mastodon.)