-15 avoid for adjacent enemies. Effectively this gives a +15 hit to the hexer in up-close battles. There are some situations where you could potentially put your hexer in the middle of multiple enemies, thus giving allies the boost as well, but overall this skill isn't especially helpful for a class that will probably be attacking from range as often as not.
Anathema - B
Very good skill, and seems to be underused judging by the skillsets assembled here. Making potentially several enemies susceptible to criticals from even ordinary weapons is very helpful. Anathema can be a key piece of some pretty scary combos, especially for Henry who also has access to Wrath.
IF I had to use one, Hex would be better IMO. Even though you have to be in their face, most of the time, your Sorc/Dark Knight can handle it, obviously Dark Mage isn't going to last, but it is still doable.
I'm pretty sure both of them stack up so in the end, as "just other skills I have that I don't have any other skills" this is a good skill.
That's how goddamminity damn good that god damn game is. - AC (GCN)
More crit + area effect for self and supporting others makes Anathema a B in my books. If Sniper's Hit +20 is C, Hex is a C at best. What's stopping me from giving it a D is the fact that your other units can also benefit from Hex if fighting close together.