Is it safe to do breast augm or reduction on someone with diabetes, since they say healing is not as good?

Yes, if... Assuming the diabetes is well controlled, breast augmentation or reduction surgery can be done safely. In the longer term, patients with diabetes do well after breast augmentation surgery.
Safe as long as the. Condition is under good or optimal control prior, during and after the procedure.
Safe but higher risk. It is still safe but does involve a higher risk of infection and wound dehiscence. This may depend on the severity, and extent of your disease as well as the control as reflected by your a1c count. Discuss the relative risks i with both your endocrinologist and surgeon. Peri-operative management is very important.