That is true. Hmm, well I would say it would be easy? While I know nothing much about web code, wouldn't it be possible to have the "like" function for that user disabled/greyed out? And if statement if you like. If logged on users name = submitter or groups name then no like
As Lenmaer said, anyone can just proxy in and like themselves. Or just logout and like from their own IP (system doesn't check for this). Or just use their phone on a cell network for another IP. All sorts of ways.
It's not really solvable, because this is a public tracker. If you restrict likes to only logged in users, I fully expect them to go virtually unused because most public users are lazy as hell or untrusting of an account system. Conversely, if it's available for anyone to use, it will likely be abused a ton. Not that it has so far, it seems, but it's still there.