Yeah, a balanced diet is enough.
I would personally never give a salt lick or any kind of vitamin supplement to any animal, unless a vet deemed it was necessary that they receive supplements. I think that a salt lick has the potential to be harmful if the hamster excessively chews it, as they'd be ingesting a LOT of salt. I just believe in feeding pets the most natural diet possible, with as little processed junk as possible...yes, I consider those licks to be processed junk.
But I don't believe in taking vitamins either, myself.