Hit rating is definitely a concern for death knight tanks in Ulduar gear depending on what drops you get in what order. the stats on tier 7 don't mirror tier 8 very much. The hardest item to replace is
[Valorous Scourgeborne Legguards] with
[Conqueror's Darkruned Legguards], this gear upgrade is the steepest drop in hit off a single upgrade in Ulduar. Overall tier 7.5 had 73 hit rating on all the gear while tier 8.5 has only 41 and is only found on
[Conqueror's Darkruned Faceguard]. This is slightly balanced if you pick up the badge neck and belt along with the hit wrists and boots that drop in 25 man as well, of which all drop off non- hard modes.
I would advise investing in the 2 badge pieces and trying to use
[Vivid Forest Emerald] as a cheap alternative to pure stam gems to stay at the hit cap.
////edit: on a side note an interesting thing I noticed the swap in avoidance stats is very peculiar... tier 7.5 has 190 dodge, 153 parry while tier 8.5 has 165 dodge and 227 parry. Is is possibly a way Blizzard is nerfing our avoidance scaling by putting more parry on gear instead of dodge? Since parry doesn't yield as much avoidance as dodge for the same Ilevel it could be a sneaky way of keeping death knight tier gear from giving them to much avoidance.