Based on a few factors from the clip -- check it out!
I find it highly unlikely that Morrisey's Doctor is actually THE Doctor. He's a bit too much of a caricature, a bit too arrogant, his sonic screwdriver doesn't really seem all that sonic and most telling of all: Neither he nor Ten recognize themselves as The Doctor. So yeah, pretty likely not the Doctor. However, some people have come up with a deliciously, totally Rusty in all of it's cracktastic glory, theory that while this isn't the Doctor, it *is* a time traveler and is actually the Doctor that River Song knows. (I know, I know, logic pretty much says no because her dialogue implied that she knew the Doctor as our Ten, but hey, I said it was crack and au-crack at that!)
ETA: Hah,
It's possible that Morrisey's Doctor used Tennant's Doctor as 'his' Tenth regeneration thus leading River to believe that she did 'meet' him or does know him. Since Tennant is leaving, River will never really meet him again, so this would fit with canon.The thing is that it makes SO MUCH SENSE. Morrisey's Doctor (from now on MDoc -- thanks,
I'm in no way saying this is going to happen, just offering possible explanations :D I would love RTD to death if he did make this happen. It would also get Moffat out of the mess he's currently in with the River Song arc and David leaving.
Being serious for a moment, if this crack theory actually had any basis in reality, I have to say that while I wouldn't wildly, obsessively ship River/MDoc as I do Nine/Ten and Rose, I could so see myself adoring and getting a huge kick out of them -- they'd be amusingly arrogant together. Yes, I know I found River abrasively arrogant when Moffat wrote her, but man, I bet that with Alex Kingston's undeniable charm and talent, Rusty would write her as amusingly arrogant as he did MDoc in this brief bit. Together and under Rusty's pen and vision, they'd be a hoot.
So, I've decided that even if it's a lonely fandom of