I never sensed Mr. H resents Mac for not allowing Bloo to be adopted so he could finally be rid of him. I always saw it as he was just such a strict rule follower, and the rules include Bloo being put up for adoption if Mac doesn't come visit right after school. And, being Mr. H, he's just very strict about it.
Because when Mac does arrive, even when he's running late, Mr. H shrugs it off with a "Ok, very well then" type of attitude. I'm not recalling him ever having the attitude of "Fine, you win", or just disappointed that Mac showed up.
And yeah, he definitely treats Mac just like he does with everyone else- wanting him to follow the rules to the "T", and getting irritated when an exception is made.