For healing spell it does affect them nowdays. It has been changed a few chronicles back so you can critical in healing and wild magic make you magic crit more!
I am also sure that you can do critical with mana burn yet i am not sure but i think that WM helps there also!
On what rate would be calculated the critics of Mana Burn then? While it may be considered as a debuff rather than an attack, it's certainly not a physical skill.