Frankia is the bacteria that builds nitrogen in the soil. You don't buy it, the plant makes nodules on its roots so that the nitrogen from the air can become nitrogen in the soil.
A funny thing happened in the last year. My wife wanted me to switch a goumi plant and an autumn olive tree, because the autumn olive was too tall, and blocked sun for her tomatoes and flowers. I had to hack it back pretty hard to get it through the gate and to the back yard. Perhaps I hacked it too hard, because combined with our extremely wet autumn, I noticed that there are turkey tail mushrooms and split gill fungus on it now. Split gill is a parasite without practical use so I will just burn those branches or put it in the green recycling bin. Turkey tail I will use medicinially. I guess there's my answer.
In my area autumn olive tend to have lots of turkey tail as you mentioned as well as some variety of white toothed fungus (doesn't look like an edible variety to me. They also get a kind of white, fuzzy, cottony fungus that almost remind me of giant colonies of mealy bugs.
I don't think the wood holds together long enough for the slower growing, edible fungus that many of us like to grow to fully mature.
I've noticed that when I cut a branch at any height, it pretty much dies back to the crown and quickly becomes inoculated with the above mentioned fungi. The crown will sprout new growth in the spring and all will be well with the shrub. Autumn olive breaks down very fast so far as I can tell. It's not uncommon for a large branch to take only a couple years to fully decay. After one season, the wood gets super spongy, which is one of the reasons that I like it for building hugelculture stuff. I think that's it's role in nature... get in, get out, leave nothing behind but better soil for the hardwood trees to grow in. I really like autumn olive and use it for many things around the property. If you find a good fungus variety for them please be sure to let me know.
Split gill mushrooms are edible. I have seen recipes for Thai curries and recipes for stews, but I haven't tried any yet. Next time I come across a bunch of split gills I will incorporate them in a mushroom broth.