I have applied wax or polish (non-abrasive...I only use Zaino) on all my vehicles for years living in states noted for a lot of sunlight (UV rays) and have never had a problem. In fact, the stickers on my vehicles are in good shape and show no fading, but the stickers on my 2 years old popup are starting to fade; probably because I have never zaino'ed the trailer (or waxed it). (Maybe I should?
From Meguiar's website forum
You can wax over vinyl stickers, decals and graphics if they are smooth and glossy in appearance. For those that are matte finished it's best not to wax over them, but we have seen some really good success with Gold Class Trim Detailer lightly applied to matte finished graphics.
A couple of things to look out for:
Pointed edges on decals can be prone to lifting if rubbed over too often and once they lift, it's pretty much game over for that decal.
Dark colored graphics against dark paint (think red on black, etc) may show dried wax along the edges that you'd have to clean up with some Quik Detailer and a soft brush. Not a serious problem, just a little extra detail work.