Does Rosacea and Acne have an effect on the growth of facial hair?

Acne, Rosacea, & Accutane most likely have nothing to do with sparsity of your facial hair. It probably is your genetic constitution, but the best approach is to check with an endocrinologist.

Two reasons can explain this. First, the severe acne could have scarred and destroyed the hair follicles. In this case, hair growth would not be possible. Second, you might have diffuse alopecia areata of the face, which can be treated. I would visit your dermatologist and get to the bottom of this.