I would assume since theres an attack roll, using it offensively would mean it can probably crit an undead, but could it also do a crit heal? Does anyone have any proof if the answer is yes?
No, because "critical heal" is not a thing in Pathfinder.
The section on critical hits specifies that you roll your damage more than once. Since healing is not damage you don’t roll that twice. The section on spells also specifies that if the spell causes ability damage or drain, that is doubled. It does not double anything else. For example if the spell causes you to gain a condition for a random amount of time that is not affected by a critical hit. The use of the word damage instead of effect means nothing besides damage is multiplied.
This could be a good house rule.
Okay folks, thanks!