No, staph skin infections are not contagious between dogs. Do you have 2 dogs with a similar skin problem you are concerned about?
As long as your dog isn't carrying fleas, ear mites, or sarcoptic mange mites, the dog should be fine. So just make sure to treat your dog with Frontline, give a dose of heartworm preventative (to take care of any intestinal worms), and finish up the antibiotics. And a dog that is stable on the Cushing's medication shouldn't really be much more susceptible to problems than another dog.
Yep, I think you should be just fine. I'd be more concerned about the Cushing's dog being so hungry she eats the turkey before the rest of you get it! : )
I had a Cushing's patient once who opened the refrigerator (it was a Jack Russell) and ate an entire stick of butter. Didn't phase her at all. So guard that Thanksgiving feast!
Glad I could help. Have a good evening!