To my knowledge allergies in pets typically show up as skin and ear problems. I've never heard of an allergy to catnip, but that doesn't mean it doesn't exist.

Although from what I know 'kitty acne' is usually more like blackheads on the chin, not red, and raw areas on the mouth. Has you cat been to the vet recently for this? and were the teeth checked then? Teeth problems frequently cause red raw areas around the mouth and gums.