I've had a play and I've found a grip where I can comfortably (for a while at least) hold the DS4 using the left grip so my thumb can access the left stick of the d-pay, or the right grip where my thumb can access the right stick or the face buttons but neither are good for L1/L2/R1/R2 and the angle is oblique so I've be surprised if the camera could track the controller well - or not at all if I'm waving my about about.
Well Nav only has minimal buttons so won't need all the shoulder buttons I suspect it will be used for little more than moving the player around so DS4 should suffice...and the PSVR won't want to track the DS4 in that scenario because the Nav isn't trackable anyway. I also think they will likely design the games with no Nav controller in mind (or at least try to avoid it's use).