[zdunn]

No. Unfortunately, the fediverse has kind of given up on the idea of a single identity using a variety of services. Every new ActivityPub services wants to own the user account and the interactions are one way or extremely limited (likes/reposts).

[bookwyrm-social]

You're correct that each server has separate accounts, and you can't log in to, for example, but mastodon and bookwyrm and pleroma using the same account. You can do more than just like or repost though - a bookwyrm user and a mastodon user can do a variety of things like follow on another, send DMs, and reply to each other's posts.