No, it's not. I've just finished the game with a character who had no coercion skill at all.
If you want all the achievements, it is, otherwise not really. Certain events are easier with a high coercion, but everything can be done somehow without it, except the achievements. (This isn't true - see below).
It's noteworthy that, unlike coercion, most other skills can be assigned to other members of the party, doesn't really matter who makes the traps.
To clarify, first, you can't get all achievements in one play through anyway. You'll have to play several characters through to get them all. Any single character doesn't have to have coercion.
Second, with high enough strength, you don't need coercion to pass intimidation checks. With high enough cunning, you don't need coercion to pass persuasion checks. So you don't need coercion even if you want all achievements, although you'll need to do some careful planning about which characters will have the attributes to acquire those achievements.