This sounds like a question for Tulsa-Dan as he has given me lots of advice in the past. But I have read a few books and Trudy is slightly older than your guy. I had the same concerns as you did with my girl and I have come to believe there growl sounds alot worse than it really is, that is how they play, the dogs body language of course is very important. When Trudy is playing with other dogs she usually has her front paws down bum and nub up in the air wiggling around, but the sounds that come out of ther sometimes do sound quite ferocious!! But I have chalked it up to the fact that she is vocal.....If he seems stiff and is truely snarling aggressively, then maybe when he exhibits such behavior you need to leash him and take a little time out. Also it has helped me alot to teach Trudy the command "enough"...When her and I are playing or even when she is playing with other dogs she knows that enough means stop what you are doing sit and chill for a little bit. This command is fairly easy to teach, easier than i thought it would be....
Also I have learned that the best way for a puppy to learn how to play appropriately is from another dog. They have their very own language one that us humans do not understand....I know sometimes it could make you a little unnerved but I wouldn't be too worried, a big dog will put him in his place, he will learn very quickly what is appropriate and not appropriate.
So I wouldn't ban him from playtime with other pups just yet! He's just a wild man!!

I wish you lived closer I would let Trudy and your guy play together and you would see you don't have the only little 20lb dog who thinks he's a tiger!