Yes; their actions are coordinated. If user A and B are in a SharePlay session and user A seeks forward user B will see their video seek forward as well. Your player UI should already be monitoring for changes in player state (play/pause, playback position, buffering, etc.) and update the UI accordingly. But even if you don't, you should still see one user affecting the other users player.
atommclain
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
User for
From
New York, NY, United States
Post
Replies
Boosts
Views
Activity
Even if you have the profile, you won't be able to use SharePlay with the iOS 15 RC.