"If indeed it is real ivory, I would not smoke it, period. Two basic reasons - both of which have to do with heat. First is, do you remember the smell of a visit to a dentist twenty years ago when the dentist was really grinding away? That is what it would smell like to smoke. Ivory is a tooth. It is made out of the same stuff as the ones you are/were equipped with."
This was an old thread but I agree, Acme. The same holds true with materials like antler when incorporated into a bole. Both of these material give a hint to this fact when being worked as knife handle materials, far more so with antler. Ivory only gave off odor anytime tools were not sharp. Heat from sanding or drilling does not bring out the strong side of their natural beauty. If some one smoked them long enough to build up carbon maybe. But whew. Those would be some bad smokes, in my opinion.
In my experience you do have cracking with ivory exposed to light, humidity, and heat. While it may be yellowed on the exterior, ivory is white when the surface is removed unless it has been scorched or directly exposed to flame. In such a case you just have to cut into it and see. I have been told it actually weathers to black if left for years in the elements.
To me there would be no problem with using these materials as spacers or stems on a pipe. Just where the cherry is.
Using solvents is always going to be something you need to test with if at all possible before using. I have no experience with using anything but tools on ivory.