Emeraldgreen - Why not just contact your vet and see what he says? Do let him know if $$ is a problem.
My employer's cat had a dark spot which he would lick at, and it would bleed a bit. The vet had a look and was not concerned...he said it would go away. I think it might be a hematoma...and that MIGHT - MIGHT be what Paddy has if there was a lot of scratching going on. That could raise a blood blister.
Is it hard? Squishy?
HUGS - all will work out.
"You can say any foolish thing to a dog, and the dog will give you a look that says, 'Wow, you're right! I never would've thought of that!'" -- Dave Barry