Am I getting this right ? (because I have 4piece and feng helm and kings chest and I came to this conclusion too, but I'm sure I'll find here confirmation on the reason why to do it)
Bloodseeker only has 323Haste, and you gain 197haste via reforging the crit away on dread shadow. 127haste lost is not such a big loss is it ?
So assuming you benefit fully from the hit and regain your expertise elsewhere, it should be an overall gain.
Then again, try it out with your own stat-weights if your want to be thoroughly sure