Zechs still doesn't like Grimmjow, but he also feels like he owes him a great debt. After all, Grimmy convinced Tyki to get over himself and come back when he had cold feet before the wedding. They'll probably never get along - and Zechs doesn't like it at all when Grimmjow tries to push his boundries - but he accepts his place in Tyki's life. And, he'd trust just barely enough to watch their backs if necessary.