Isn't the "they're all actors and robots" thing a censorship thing; a way to get spooky monsters in a kids show? Like how SU says Gem don't have gender so they can get lesbians on Cartoon Network?
Alternatively, you could turn to quantum mechanics. The Baskervilles could have a big twist in a later episode where it is revealed that they really ARE monsters after all. As all but an early 3 episodes are lost from existence forever, we have no way of confirming whether or not that is the case; we have no way of observing the entirety of the series to be certain whether or not that twist exists. Thus, we may behave with the assumption that they are revealed to be monsters, and be no more invalid in that assumption than we would assuming that this twist never arises at any point in the series and they are not monsters.