Doctor says Rub RetinA on stomach to tighten Skin. Does this really work after Liposuction?

I do not think that there is any evidence that this will help at all. Please save your money. The amount of skin tightening on the face with RetinA is incredibly small, the amount that you would see on the abdomen after liposuction would be even less. 

Retin A is a topical agent used to regenerate portions of your skin which thin over time. I have not heard of it used for liposuction recovery, nor would I reccomend it.

Tretinoin can be used to help fine lines and wrinkles, as it is one of the very few topical creams that have shown benefit by promoting collagen synthesis.  However, I am very skeptical of any "skin tightening" you could get from this product on the abdomen.  If you were to get any results it would be very minimal and require months to years of treatment.  I would consider body radiofrequency or ultrasound treatments.  On the body Thermage is a good option if the laxity is surrounding the belly button.  I wish you the best of luck, Dr. Emer.