Just so you guys know the difference, a colostomy has practically nothing to do with the anus.
Basically, for whatever reason the colon can no longer be used due to medical reasons so a hole is made in the abdimon, not to far from your belly button. This hole doesn't act like a anus because it has no muscles. When food goes through your digestive tract it ends by leaving the intestines and going out the colostomy hole. I don't think there would be a problem having anal sex but the original question mentioned using the colostomy hole which could pose some problems. Anal sex would probably be made easier since nothing ever gets down there, there would not even be a need for enema's. Nothing but clean sailing.

If you don't feel comfortable asking your doctor, maybe you could at least find a medical web site to ask open questions.