^^^ This! My personal dogs are never loose together unsupervised, and they've lived together for the past two years. I sure as heck wouldn't them unsupervised with dogs they've only just met.
Same thing is true for my dogs--sometimes my dogs have lived and played together for 6 or 8 years. In the yard they are supervised and often muzzled as well--if one dog plays too rough and hurts the other dog retaliation is often instantaneous--I'm pretty quick but I don' rely on being able to get across the yard to stop two grumpy males from fighting.
My dogs do not go to dog parks because I firmly believe that they are accidents waiting to happen. Far too many people who pay no attention to their dog, can't read their dog, think their dog "just wants to play" and always seem to own pushy, ill-mannered dogs.
And my dogs don't go to day cares for much the same sort of reason. Not all day cares are created equal--but too many have helpers who don't know enough about dog behavior to be effective are maintaining peace in a herd of boisterous puppies.
Unfortunately stuff like humping during unsupervised play (geeze--unsupervised--I want my dog supervised if I'm paying someone to watch tem for me.) can adversely affect the humpee's attitude toward other dogs--humping can be relatively benign or it can fall into a category of behavior which is just pain bullying.
And Caleb Cox had a good point--just as Dobes are not good candidates for unleashed dog parks--I don't think they are good candidates for day cares.
People talk about how Dobe temperament has "mellowed" over the years and the breed has lost its "sharpness". I think that's less true than the fact that many more dogs (and breeds) in their early days were kennel bred and raised--and it's always interesting to note that those dogs were very sharp indeed. But sometimes they had litter mates who were family owned and much friendlier dogs. I think that the dogs today are much better socialized and Dobes don't do well as kennel dogs, nor do they do well as dogs who are socialized primarily by other dogs--so no doggy day cares for me.
I've been lucky enough to be able to bring puppies to work with me so they saw lots of people, not so many dogs except the ones they lived with and got potty trained and leash trained pretty early.
If it ever came to having to find a way to leave a dog of mine somewhere--he'd go to a friend who a dog sit for--and who dog sits for me in exchange.
Good luck with your dog care--accidental breeding is pretty much not a possibility if they don't take intact dogs over six months but I'd want to make sure that they knew you expected to either remove your puppy bitch of the older dog who was humping her if it occurs.