Super tame. If you are worried about that you'd be horrified at how some of our sport dogs play. The only note I'd make is don't allow dogs to play with prong collars on or cones of shame. You don't even want them playing with collars that have metal in them because they might break teeth or get caught up in them and cause injury.
Yes, be prepared for a lot more animated play between the two of them once the cone is off and they become more comfortable with each other!
Bailiff brings up a good point re: collars.
I remember when I first started browsing this forum there was a thread about the dangers of keeping collars on while the dogs are at home. At the time, I discounted that advice… I had never had problems with my last dog (a probably GSD multimix) and foster dogs… so, I thought, these people must just be super over-protective and paranoid!
But, after adopting a GSD and then fostering other GSDs, I started to understand where their concern was coming from… but, I still thought it was extreme to remove their collars.
I will never forget the night that the wisdom of that advice became crystal clear. My dog and a GSD foster dog were playing when, all of a sudden, there was screeching from both my dog and the foster dog. John and I ran over to them and, sure enough, Riley had gotten his jaw stuck in the foster dog’s collar. Thank goodness I had a ‘quick release’ collar on the foster.
After that experience, anytime I have a GSD foster I take my dog’s collar off and only put a quick release collar on the foster. I also started to remove the foster dog’s collar before crating him/her for the day as that was another concern raised on the thread I referenced earlier. I don't crate my dog so that is not a concern for him.