[thaumasiotes]

This hypothesis depends on the predator-prey system not yet having reached equilibrium. Animals are white in the snow because that makes them hard to see, not by coincidence. (Where snow isn't present year-round, the same animal will usually be white in the snow and brown in the summer!) If wolves benefit from being white in the visible spectrum, and their prey starts detecting them by ultraviolet light they reflect, they should respond by turning whatever the analogue of white is in the UV spectrum.

To explain the UV vision of some prey animals as an adaptation to the fact that their predators are otherwise difficult to see, you'd need an additional assumption along these lines:

1. UV vision is a recent development in the prey animal. Eventually the predator will develop UV camouflage, but this just hasn't happened yet.

2. UV camouflage is inherently difficult. (Might be true! This is the generally accepted theory for why insects, reptiles, and birds can be blue, but mammals can't -- mammals are more recent.) This is the same theory as (1), but allowing a longer timescale.

3. Detecting this predator is more important to this prey animal than ambushing this prey animal is to this predator. (For example, maybe reindeer are primarily threatened by polar bears, but polar bears mostly eat seals.)