Yes to all. Whether as part of a security force, a hint of how Awakened the world is, a precursor to The Big Encounter with the Toxic who incited it, or just as a reminder of how bad some areas of the Sprawl, even Downtown, really are, Critters are a way for the GM to give players a bit of combat without having to have any real reason besides 'you scared it / it was hungry'.
Or maybe there is a real reason, but they don't need to know that yet...