Thanks for the great questions! Since morels like a moderate level of moisture, a well-drained sandy or silty soil is often a hospitable location for them to thrive. The SSURGO data set is a great place to start if you are in the US. Filtering through this dataset and overlaying the desired soil types with forest boundary and tree stand data would be an excellent way to further refine the search.
As for the NDVI processing, I have worked a little with Landsat imagery and in theory this is totally possible. Getting the reflectance signature of the certain favorable trees seems within the reach of Landsat resolution. If you are wanting to find morel patches directly with spatial data, you probably need higher-resolution multiband imagery. Even with the resolution, you would need imagery from the right dates in early spring and tree leaf cover would probably conceal most patches. While the largest ones can grow as big as a basketball or larger, most are the size of a baseball or smaller.
I am glad to find another GIS enthusiast! Thanks again for your input.
RE: Hunting the Elusive Morel Mushroom Using Spatial Data and GIS