Oscar … would be afraid. The poor little guy has lived on his own with the assumption that everything outside his safe, cozy walls is dangerous in some way. A dog, being loud and boisterous and having a mouth full of rather sharp teeth, would terrify the poor little guy.
Poor Rumsfeld would flop near his hiding place and whine, because he just wants to be friends! It would take a lot of coaxing (or Sam hoisting him up by the collar, he’s a lightweight) to get him out in the open to meet a friendly puppy.