What material is the Blackout housing?
The Blackout housing is Polycarbonate.

Are there BacPac backdoors for the Blackout Housing?
No. The Standard Housing BacPac backdoors are compatible with the Blackout housing.

How do I tether my camera since there's no longer a slot in the backdoor for me to loop the tether through?
See this article for details: Tethering Instructions For Housings Without a Slot on the Hinge of the Backdoor.