If memory serves, they're from various stock cartoon sound effect packs and sample CD tracks. Some of them are by Mel Blanc but there wouldn't be a single voice actor.
SM64 is hardly the first time Mario was voiced, though! Earlier portrayals like Lou Albano's are still fairly popular.
But i do wonder if the stock sound effects are the earliest by date of recording, making one of those voice actors the earliest chronologically—or is that what you meant in the first place?
As bad as Hotel Mario is, I don't think Marc Graue should be left out in a list of Mario voice actors either, his performance is the reason his lines are still constantly quoted and memed today because damn is he so quotable.