HA! I just arrived at my mom's house last night and she recently acquired two cockatiel and a lovebird. Rhys was so scared of them last night, he tried to stay in the opposite end of the house! Poor guy! (They didn't bother Andy in the slightest)
Until - he discovered all the yummy birdseed under their cage - yum, yum! Like a smorgasbord!
My mom's dogs used to eat spilled seed from a now-deceased cockatiel all the time.
As far as outside birds go, I don't know. I could see where droppings and mold might be a problem.