the bottom line is that grima is not an uruk tracker. so he can't take advantage of the key cards in the deck. plus
vengeance eclipses his ability and strikes at the heart of the deck by instead of removing the freeps cards, exploiting them for major pumps. say you are skirmishing gorn with his bow, his sword, saga of elindil and a search card. one
vengeance means a free +8. grima would strip that away.
but whatever, its your deck, playtest and see what works best.