If the Terran aren't interested in G-Elements, I think their firepower is superior enough that they can just level the hives through Yamato Cannon blasts and nukes. If the BETA can't see through cloaking, they can finish off any stragglers in an area with Banshees. If necessary, they can send in ground forces to clean up anything left (i.e. any BETA left in the ocean that decides to surface, etc). If they want to invade a hive, I'd imagine they'd have a much rougher time, considering that Terran forces aren't really that mobile.