first off...I have never used Pecan hull mulch. Some thoughts. First, most likely this is "raw" material, that is, has not be processed except to break up. A concern is what else is in the mulch regarding critters, bacteria and molds.
Secondly, nut trees and, perhaps the hulls of their seeds (nuts) have materials that often inhibit growth of other things. I know nothing about the pecan.
If you were determined to use it, consider some sort of sterilization, say roasting in oven at 250 deg (F) for about an hour or more. I doubt the aroma would be as bad as other things we sterilize in this way.
Then, try in one or two inexpensive but well growing orchids and see what happens. I know there are other more knowledgeable on this forum that will give better advise.