I have to chime in here, there is absolutely no proof that humping has anything at all to do with dominance. As a matter of fact, the most recent studies show that it's done in play, periods of anxiety, over excitement and just because it feels good....or so the studies show.
I absolutely do agree thought that it has to be stopped immediately by the responsible owner. Allowing dogs to 'work things out' is just not smart and usually ends up with someone's dog either injured physically or 'changed' in other ways. Every moment that a dogs eyes are open they're learning.
If they learn that humping is rewarding in some way, they'll likely add humping to their dog park interaction repertoire. If a dog feels threatened by a dog who's rudely 'wiggling away", while the owners stand by and do nothing, well, that dog is going to have to change the way that they respond to rudeness.
Any way you slice it, humping is rude and not often tolerated by other dogs, however it's intended by the dog doing the humping.
As for the question about should any DA dogs go to a dog park, I really don't see any circumstance where this would be safe for either the DA dogs or any other unsuspecting dog who they just might 'accidently' meet.
I happen to adore the OP's dogs, have never touched them or talked to them but feel a genuine affection for both of them. I'd hate for them to be blamed for an incident that was not their fault simply because they're at the wrong place at the wrong time and someone elses dog starts something.
DA, mildly DA or just not tolerant of other dogs...not the right fit for a dog park with so many uncontrollable variables and one of the many reasons that you'll never see one of my dogs at an off leash park.
JMO of course...