Considering that goldfish can live in temps up to and possibly beyond 91 degrees... I don't think it would be a problem.

I know of plenty of people who put one or two goldies in with their tropicals to take care of snails (goldies are Awesome snail eaters). I myself used to have a mixed tank like that.

Just remember, tho, that goldies are one of the messiest fish out there and you'll need good filtration. I would say a good filter that's rated so your gallonage falls right in the middle of the range at least.