Forget the confusing gaze, what's really puzzling about the above image is the 8 RHD creature with average intelligence chosing to become a wizard.
Anyway, umber hulks just aren't that good. Their chassis is decent, but aberration HD are very poor, they're slow, and they probably can't use weapons either. Furthermore, any utility abilities are nonexistent, unless you count very slow tunneling.
Confusing Gaze will hit allies unless you invest in the appropriate feats, as it lacks the convenient 'immune for 24 hours after a successful save' clause. I do admit it's a nice no-action debuff at ECL 8, even though the increasing numbers of immune enemies at higher levels will be frustrating.
In the end, I think +0 is best, with a case to be made for +1 or -0. Do discuss.
Truly Horrid Umber Hulk
Lack of creative naming aside, don't play this. -0 LA for obvious reasons.