>>Uehrek+(OP)
Sure, I would imagine such clauses exist to make this sort of thing a lot cleaner and easier. I also don't see how it could be reasonable to assert that in the absence of such a clause, an actor owns the rights to the voice of that character and no one else can portray that character with the same or similar voice without their express consent. Not everyone who creates something is signing Hollywood acting contracts with their hired actors, and I just can't see any court asserting that "CoolTubeProductions YouTube Channel" can't continue to produce more animations with their "Radical Rabbit" character just because they didn't have that sort of clause when they hired a voice actor at their college for the first year.