I have a German Shepherd and my pitbull. My German Shepherd is not neutered and my pitbull is. They love to wrestle and growl at eachother. My pit seems to like to grab the shepherds legs and hold on. Luckily for me it seems to be all in fun. But we do interrupt them when they play. When they become intense or really at the peak we call them apart, have them sit, relax until maybe their breathing has slowed then allow them go back and play. We also supervise all their play time.
My suggestion to anyone w/ a multi dog home is not to leave them alone esp if they have had fights. Your best bet is to crate them both or atleast one of them while not at home. Or invest in seperate dog runs if that is an option. Anything can cause a fight and if noone is there to stop it the results could be devestating for your dogs and you.