Before I answer I think I should say, I myself do not own any hermit crabs per se, but as far as the animals itself goes, if they are relatively like most all others etc. it should be fine if not beneficial and a visual treat with the contrast of the bark and the sand etc. from what i know about hermit crabs is that they actually like climbing which means wood!
most of all,....do a little home work which is what you're doing right now trying to find out about your creature as much as possible, i think a regular book from your local pet shop or even better, ORDER 1 FROM HERE! That would be the ticket on finding the answer and in my opinion? i've found very few animals that don't benefit from a little humidity and that is only how much moisture you add in the first place. sooooo,....all in all? i think your idea is a good one and try to remember to add a few as in a good amount of climbing branches for your crabs and i think you have done and are doing a bang up job trying to find out all the info and taking care of your animals,...I "SALUTE YOU"!
C-YA and let me know how it turns out!
C-YA & "HAPPY EASTER" and have a good time with your HERMITS!
THE 'ZODIAC' SNAPPER!