Technically, aliens and pterosaurs are cast members, but there are no kittens on Torchwood, so this makes the kittens OCs. (Or OFCs = Original Feline Characters.)

Hasn't Ianto suffered enough, thanks to the kitty-cock manip and being repeatedly cat-ified in fiction?

Torchwood isn't Bewitched, where this happened all the time. (Poor Darrin.)