if you load a PeerTube video in Mastodon/Pleroma/Misskey etv and click 'like' from there the like federates back to PeerTube and shows up in the total like count. I just double checked this was true after seeing this post since I was worried the functionality might have broken. I am not sure if there is any other software that supports sending a dislike back to PeerTube tho. But there is no reason that any software couldn't enable that quite easily.