Just my experience.....
A neighbour of mine a few houses down has an intact female (some kind of boxer mix). Of course her owners don't care and let her wander while she is in heat. Now this dog has played with my dog many many times before with no problems. Well she wandered into our yard while in heat, and my girl (who is fixed and apparently is a dominant female) went ballistic and had that dog by the throat the moment she came into reach. The second time that same dog came over, I went out to get mine before a fight and the dog in heat tried to mount my dog and all hell broke loose again. I had to go talk to the owner and tell him that I was worried that his dog was going to get seriously hurt (among possible other things) wandering around in heat.
They still play now when she gets loose, and as long as the other dog is not in heat everything goes fine
Guess it could go either way depending on the dog