Just make sure your vet surgery knows he has FeLV. Other than that, this surgery is as routine for a positive cat as it is a normal healthy cat. I am assuming even though he has Leukaemia, he is normal at the moment? Most neuters are accompanied by an antibiotic injection, so that will guard against any infections. We have done plenty of surgery & dental work on cats with FIV and/or FeLV, and they've been fine.