They'll work - the granulated kind mixes in easier, but the powder works fine as well, in my experience. Just take a little extra time in the blending, and use a bit less. I usually blend in the food processor, but when I use the powders they tend to fly up in a small cloud when blending. Thus, if I'm using powdered items, I prefer to dump everything into a big ziplock or one of these large 2-quart Dixie or Ziploc brand plastic throwaway tubs and shake the fool out of it. Not a glamorous method, but, hey, it works!
BTW, my favorite shakers these days are wide-mouth pint jars using two flat lids and one ring. I punch holes in one flat lid, set another flat lid on top of that one, screw the ring on over BOTH lids, and voila - air-tight storage. Unscrew the ring, remove the one unpunched lid leaving the punched one on the jar, screw the ring back on, and voila - the shaker. May be an old idea, but it works for me. The temptation is to keep them out on the counter looking all pretty, but light is an enemy of spices, so it's better to keep them in the dark somewhere for storage.
Keri C, smokin' on Tulsa Time