Sounds like a lot of big dogs play nice with their smaller counter parts. I have found that true when meeting some big dogs and some get down on the ground to get to play with the smaller dogs.
Georgie actually did that a lot when Jackson was still a puppy. She would get in the down position and swat at him and let him jump on her. She sometimes played rough too and we would break it up until we realized neither were hurt and he was coming back for more so we just really watched them until he got to her size.
I have a 6 month old black lab and 1 month old pomeranian. They like to play with each other alot. The pomeranian would always try to beat up on my lab. There were some times when the lab got a little rough, but nothing serious.
I would let them as long as they were good friends and played well together. My donkey plays with my Dobe bitch but doesn't seem to like my dog, so I have to keep an eye out if Duke joins Gretchen.But you have to be careful with longears and dogs or other small animals for that matter....longears is a term for donkeys,mules and hinneys.