The emergency vet is confident that the problem was a bad reaction to the anesthesia and in future we'll have to make sure we communicate this before he has any other surgery. There are other options, so this shouldn't be a huge problem, just something we need to make sure they know about. I was thrilled to know it wasn't a genetic clotting disorder, one of the scary things on the list of possibilities. Turns out his blood clots just fine.
We'll keep him kind of drugged up for a few days, and Mr. Dog has to check the incision every day to make sure it isn't seeping or infected. The drugs make him kind of sluggish and lazy. They also make him a bit less coordinated than usual, so he kind of staggers around a bit more than normal. It is a little bit amusing actually. Other than that, he's more or less back to full speed, but a bit lighter and less pornographic looking when you see him from behind.