I've spent some time testing add-ons in VR today. It's a mixed bag - most of the aircraft that don't work seem to be a texture issue. For example the freeware Aeroprakt A22 Foxbat, which worked perfectly in P3Dv3 with FlyInside, doesn't appear. You can hear it all working just fine, and the lights are there (nav, strobe etc) but the aircraft image itself is missing.
That goes for all views. I had the same with the A2A WoP A6M5 Zero. These are older models, of course, especially the Zero.
I also had issues switching aircraft - P3Dv4 would invariably crash once I changed to a different aircraft. I'm also finding the scenery textures very light and washy in VR, and some of the models textures, too. The Alphasim B-24 Liberator actually worked well, but the textures were way too light. I had this with the Alphasim Blenheim in P3Dv2 - and Dave Garwood sent me an updated model file, which sorted the problem very well, so it wasn't the actual textures that were at fault, but some setting in the aircraft model. I don't know my way around them well enough to have any idea about that.
Tom Piglet's A-29B Tucano worked excellently, v4 and VR, as did the Icarus Gladiator - though I realised the FM is really awful in that, so I won't fly it again. Had it for years and never realised!
Although the sim is running very smoothly, the VR view sticks on occasion, and the view through the canopy is often poor - as if someone had cleaned it and left it smeary.