Well, i think that a Act 2 Holy Freze merc is the best, as he Slows all enemys, Even the Cold Imunes.... But i think that a Prayer merc could be useful as well, But I like the freze 1 most..
As for the Frozen armor, then i think yes, its 1 point and it helps while teleing... If a Monster hit you, it freze long enough for you to be gone..
~Shadow