Will this make them more visible to predators or hunters?
I suppose it depends on what spectrum of light it interacts with, but that seems unlikely. These aren’t glowing in the dark - they just reflect light back that is shining towards them.
Yes, it seems to be retroreflective. Which means that the reflection is only aimed at the light source mostly. That also means the most visible they’d be is around sunrise and sunset and moonrise and moonset because the predator could be standing between the antlers and the sun, meaning the sun is being reflected right back at the predator.
When the moon is overhead though, it’s still going to make them stand out. The reflections aren’t perfect obviously so any scattered light from the antlers would absolutely alert predators.