Its combined ualaa. If i chains of ice off just one character and then another, the second toon still gets affected by DR.

It REALLY doesn't matter which dk does the spam of chains of ice. I just space it out across all the dks via round robin so that the rune usage would be more "even" across the team. Also it helps out for if one dk is cc'd or dead.

It's not really intuitive for that tho, i just prefer to keep the rune usage spread out. Its not really even needed in the spam if you're to keep spamming howling blast, HOWEVER...

I've found that there are a few instances where i can draw out a pvp trinket use from a healer with it in arenas, which lets me set up for a big hungering cold/single target swap.