Re: What a great message board!
Welcome to the board! The Smokies is my favorite place to fish but can be a bit difficult this time of year. Go to the high elevation streams and you should do fine. The absolute best advice I can give you is to stop by Little River Outfitters in Townsend. They will help you with a fly selection and steer you to some good spots. They are easily the best shop I've ever been in.
About the small mayflies you mentioned, you can fish them but honestly the fish probably won't actually be keyed in on them so slightly larger and easier to see flies will still pick up plenty of fish.
The best technique for nymphing in the park is to fish without indicators by highstickin'. The water is kinda low right now though so sticking with small dries and terrestrials should work just fine (although the nymphs WILL still catch a LOT of fish).
Finally, be sure and pick up some Green Weenies. If it happens to rain the day before you fish and the water is stained, they will work wonders. Some of my best days have been in summer when the water was "up" and stained from the previous days afternoon thunderstorms.
Good luck on your trip and let us know how things go! I'll be up there myself for the last half of next week so leave some in the creek 8-).