None of my dogs are allowed to play with each other. When I bring a puppy home they are kept crated or leashed until adulthood and at that point they are completely focused on the people in the household. The other dogs are just there, each knows their place and their job.
Terry, that's a large part of why many handler's can't handle their own service dogs. Because they come from households with 'pets' and want to teach their service dog like a pet.
I don't mean that you can't play with your service dog, that you can't love on and give attention to your service dog (or working dog since I have worked with protection dogs as well) You should love and play with your service dog... but play with other dogs is a risk that I as a handler am not willing to take... with their training and with their safety.