The Hunter keyword works similar to the Ambush keyword in terms of multiple instances on the same character. If a character who has Hunter 3 is given the additional gametext Hunter 1, that character has both Hunter 3 and Hunter 1. Since it's not an option to add that strength if skirmishing a non-Hunter character, it would work the same as Hunter 4, but it is still two separate instances (Hunter 3 and Hunter 1).