Actually, I would put them in the Kingdom "Ineffigiatus" with the ghost types simply because they would not fit anywhere else and it's a little much to create a whole new kingdom for just 2 Pokemon.
There's acutally 15 artificial Pokemon:
-Grimer & Muk
-Voltorb & Electrode
-Porygon & its family
-Banette (basically a Shuppet inhabiting a doll)
-Trubbish & Garbodor
-Golette & Golurk
It doesn't seem appropriate to put most of them along with the ghosts, since most of them have physical forms.