You can limit slavery to sub-species - so you could have the Intelli-Lizards as residence/citizens, working your labs, while their altered cousins, the Rockgrubbers, are Chattel slaves.
And yes, I think you can enslave your own species if you have the right ethic/civic, although I am not 100% certain on this as I don't do it, I only enslave worthwhile Xenos.