Kelly,
I am sure that it might work with lots of grease. However, when I want a hopper pattern, I use a hopper pattern like Lawson's or Whitlock's, etc., etc.
I know that Gapin(sp?) believes it can be used as such. I visited with his son not many years ago and discussed the Muddler. He said it was used primarily as a sculpin pattern and not as much for trout as for other species.

I wonder if folks who use it during a hopper fishing opportunity are really fishing it as much as a sculpin. When you fish it, do you strip it in like fishing a streamer?