Am i able to get a breast reduction when I have severe chest acne?

It would probably be best to at least get the active lesions under control before having your reduction. The chances of having an infection with the surgery are still very low. But it is better to be safe than sorry. The acne does not have to be completely clear, but the severe and actively purulent lesions should be controlled. 

Having active infection in the skin around your breast will increase your risk of infection, which if it occurs increases your chance of bad scars - you should try to settle the infection down as much as possible with medical grade skin care, microdermabrasion and possibly peels or antibiotics. See the link below for more information. Regards Dr Charles Cope 

If you have severe chest acne, it is probably best to get that under control before undergoing your breast reduction.  Good luck.