I find that if I'm fishing in an area with a good population of suckers I periodically catch them on pretty much any nymph (GRHE, isonychias, prince, small stonefly nymphs etc) I'm fishing as long as I'm getting a GOOD drift. My own experience with suckers is that they are a lot more sensative to any unnatural fly movement than stocked trout are. I actually use it as a barometer of sorts for certain holes I like to fish. If I catch a sucker once in a while, I know I've got my weight and drift spot on. Also, they fight great. Heres a pic of an Allegheny River Sucker I got on a prince nymph.
Fish trout flies slow and along the bottom. Sucker spawn, nymphs and worm patterns will all take them. If I'm fishing a pool with both species, suckers almost always spook before the trout.