Address shader issues on older devices

I built a snow shader (based off a Brackys tutorial) for my Oculus (GearVR) app. The shader works great on the Samsung Notes 8, but there are issues with flickering and rendering differences in each eye on Samsung Note 5. I can only make guesses at this. I am thinking the two phone render differently. Possibly single pass versus multi-pass. The shader includes a Normal Vector (world) and Dot Product.

VR Question: How do I detect single vs miltipass based on phone running the app?
Shader Question: How do I assign a fallback shader?