The revolver is the Vortigaunt's only natural predator, and the Hivehand eats up soldiers like a fat guy eats Cheetos. So, take out the Vortigaunts with the revolver. Then just take a few shots at the Osprey with your rocket launcher, then hide around the corner and kill this HECU bastards with the Hivehand. Works like a charm. And charged TAU shots against grunts will cause it to rain gibs, so use that after you've dealt with everything else, take cover, charge that stuff, and then let 'er rip!