if the copy of the statue is being used for costume purposes and ONLY HIS costume purposes theres nothing wrong with it as long as he gives credit to the makers. the makers of this statue do not make costumes, so he is not taking away from their business. If he was to sell the costume, it would be a problem. If he was to make another statue and use it just for himself, to make a display with two masterchiefs that would be a problem.
these rules dont apply in all situations and theyre my own opinion anyway. for example recasting a lightsaber you use for display to make a spare one for a costume is not cool