Actually, I doubt it. Peeves referred to him by name. And a dog couldn't give the password anyway.
Originally Posted by fawkes_07
"Oh yes, Professorhead," said Peeves, with the air of one cradling a large bombshell in his arms. "He got very angry when she wouldn't let him in, you see." Peeves flipped over and grinned at Dumbledore from between his own legs. "Nasty temper he's got, that Sirius Black."
And nobody said anything about a big shaggy black dog, so Peeves must've seen Sirius Black the man not Padfoot the Animagus.