The finish is not as critical as the temps it will be around. In following this forum for a number of years, and the dozen or so times I have read about those who have problems - is with mammoth tooth cracking. Not in the building process but in the long run.
Snake wood, some ebonies and mammoth tooth seem to crack from heat, not humidity swings as most woods can do.
I don't know if this is the answer or not, but if I were to use an expensive or rare material that is temperature sensitive, I would use a chart to find out the next size up for drill bit, one maybe .003 larger than the one recommended for the pen. Drill the mammoth tooth out and use a rubber epoxy to allow for contraction/expansion in heat and stress situations.
Some people have trouble with cross cut blanks, which is where wood expands and contracts the greatest. This happens with humidity swings. But very hard woods and some materials such as mammoth tusk/tooth and ebonies and snakewood are more sensitive to heat swings, especially if expansion is not allowed.
People (me included) have had some of these sensitive material/wood pen blanks for several years and nothing happens. These blanks go through humidity swings and temp swings in unheated and un air conditioned shops. No cracks! But after making a pen out of them - within 6 months to a year cracks develop. WHY? They are locked into position by unmoving glue. Try some rubber epoxy. Most rubber epoxies that I have seen are whitish in color after mixing. Rubber CA is black and I don't think I would use that. Also, remember to use a chart to find the next size up (but not too large) drill bit.