They are your creations, your art. If you want to use wood duck flank feathers for your parachute posts, go for it. I'm certain the flies will be effective.

That being said, I (and most of my friends who tie) will trade you bags of mallard flank dyed to look like wood duck for your real wood duck.

Use your feathers however you want.
I think I'll go tie a fly with a polar bear post now on a whim!