Did the OP not understand how a whole home DVR works? Did he not ask Dish if what he wanted was possible. From Genie to TiVo to Hoppers, they ALL are whole home DVR systems and work the way with all clients seeing the HOST DVR. Of course, with DISH, one can ISOLATE ONE Hopper from the other. I am unaware of TiVo being capable of isolating any client to ONLY a particular DVR. Yes, one can only have one HOST DVR with TiVo, but I can still see all the other DVR's in the house and can access and stream for any of the S4 and S5 TiVo's, and at least LOOK and peruse at all the recordings on the older S3/HD TiVo's (streaming not supported on S3/HD units). In other words, I am unaware of ANY whole home DVR system doing what the OP wants because they just don't see the need for it, but it would be a nice option.
This brings me to the thing I have been asking Dish to provide for many years: the ability to at least install a SEPARATE DVR like a Wally on our account for that person we DO NOT want on our Hopper network. I don't think the OP's situation or what he wants is unreasonable, but Dish should really look at this and see if they can come up with a solution or policy or business practice that can address this. It is my understanding that the Wally is allowed only as an RV box, not in the home with an existing account? I don't remember exactly.
The solution for the OP is to have TWO Hoppers w/Sling (although no multiple Hopper 3 installs allowed by Dish unless each H3 has its own account), one Hopper for the snoop, and one for him and family, then each Hopper will NOT see each other and the snoops client can not see the family's Hopper.
Let us know how you get this resolved or if you will live with it.