Should I Try Microdermabrasion for Bottom Acne and Scars?

Microdermbrasion would be a relatively conservative way to go about scar revision on buttock areas. Keep in mind that you may have to do a dozen microdermabrasion a month apart before you start to see any improvement. If you don't see significant results after numerous microdermbrasion, you may need to see an experienced board-certified dermatologist or plastic surgeon who is well-versed in the art and science of Fractional CO2 laser resurfacing.

Acne is caused by plugging of the oil glands. The plugs are too deep for microdermabrasion to be of any help.
Microdermabrasion is equivalent to a mild peel. It may help the acne medicine penetrate easier, but it adds greatly to the irritation.
The best treatment is similar to that of facial acne, with Benzoyl Peroxide in a.m., a retinoid at night, and, in the beginning, some oral antibiotics.
It is also very important to avoid tight fitting garments which contribute greatly to plugging of the oil glands (friction, sweating, etc). This may be a difficult request to a young person.
As to a helpful device, the Smoothbeam Laser can be very helpful for both acne and true acne scars (not pigmentation).