P5000 is GP104, P6000 is GP102 (the non-crippled Titan X), with the Tesla hanging out on GP100
I think the question is if you can have three GPUs installed, two in SLI, with a Quadro also being there. It couldn't take part in gaming, but I don't see why it couldn't be in there. (Maybe, the title and question don't exactly match)
Might have to swap the monitor around and reboot every time you want to use one setup or the other. And specify the appropriate GPU for the appropriate job using the Nvidia control panel.