I would just pluck them too. At least 7 or 8 years ago, I bought a drake woodie skin from a well known flyshop up in Maine. It still has so much oil that it's leached into several changes of paper towels on the skin side, and the oil has gotten onto quite a few of the flank feathers on the other side. If I need them, I'll have to pluck, wash, and dry them in order to use them. My main point is, even professionally done, they can still have a lot of fat or oil left over.

Regards,
Mark