Antlers are basically mineral deposits, and do not absorb much of anything. You have to line them, or coat them with burnt sugar to have something to absorb the tars in tobacco. Bowl Sweetener is used to build up a carbon cake in such bowls to absorb the tars.
Antlers would be a HOT SMOKE as the bowls will warm up rather quickly, and won't dissipate heat very fast. And, since it can't absorb juices or tars as well briar, you get all that into your mouth, making it hot to the taste as well. Lining antler pipes helps them out immensely, but just smoking a briar pipe makes even more sense. Its your money, however.
I don't think there are any more health risks smoking an antler than smoking any other pipe. Mouth cancer is the most common problem, but cancers of the lip, or gum, and sometimes the sinuses can occur in pipe smokers. Tobacco chewers are much more likely to develop these cancers, because the tobacco is held in such close proximity to the flesh of the lips, gums, and tongue, on a regular basis.