Actual dogs aren't sapient, so it's hard to really call them "good" or "evil". They just do what they're trained to do.
Birdo on the other hand is very definitely sapient, but it's still not made clear if she was willingly serving Valentina or just trying to kill you because she was bored. I guess the dialog leans more toward the latter, but nobody else in the game ever acknowledges Birdo, so how can you tell?