Joe,
I fished with a guide up in the NE end of the park once. I normally fish dries and told him so but, early in the morning with no hatches going or hoppers moving, he wanted me to go with nymphs, actually an IPW (which is something that doesn't show up in their catalog) and PT trailer. Like I said, I normally fish on top, but those flies caught a lot of fish, and he showed me another way to find them in the off hours - really paid off when I went back up there with friends in October after the hatches and terrestrials were done and streamers weren't making it happen.
Regards,
Scott