Yes you can mount deer in velvet, there are a number of techniques out their but the most common used are inject "perserving fluids" or coat the antlers in borax for a drying period. Newer techniques such as freeze dry (like flowers) and synthetic velvet (as mentioned earlier) are gaining favor. If you shoot a animal in velvet and may want to mount in that form you should freeze it, if their will be a delay in getting it to your taxidermist.

You can also have the velvet stripped and darken the antlers. I have stripped a few spiker (elk) over the years that we have taken and just left them to drywithout staining- bone colour is the result.

I have shot only 1 deer in velvet, it was not worthy of mounting IMO. Other then thinking it would cool to get one thathad dried velvet strings still but stripped,I haven't got a deep desire to get one in velvet to mount. That said i wouldn't pass one b/c it was still wearing velvet either.