Speaking from mostly the opposite perspective it does fall to the Tank to make sure they are keeping up on the enmity combo's, that being said there is a heavy stance within the tanking forums that you shouldn't be in tank stance if you can avoid it to do more DPS (at least as a warrior this seems to be the trend). As for your experience with the DRK there's no excuse for not using grit that I can think of. The stance doesn't cost anything to use and the dps stance consumes mana at a regular rate, so being out of Grit serves no purpose.

I think the bigger issue here might be communication between parties, I don't know if you're running with the same people every time or different groups at different times. If the latter than I'd say don't worry to much about it, it sounds like the Tank forgot to do something. If it's the same groups every time I'd say maybe try talking more with them about what you expect from them? Maybe that way instead of the party being concerned about lost dps you can all focus on how to improve it across the raid, after all Utility and helping your fellow party members has to count for something?

P.S. Not a full time raider, so take this for what you will.