When I lived nearer to town I would take all the used grounds from one of the cafes. I never experienced any problem at all. The compost pile, which was a cool one, was always full of worms. If I left a bag of grounds on the ground for a few weeks I invariably found that worms had invaded it if was moist enough. If I had too many grounds for the compost pile I would simply sprinkle them directly on the garden, around plants. Never a lack of worms.
I can’t comment on their effect on microbial life but I am under the impression that a good worm population goes hand in hand with a good microbial population.
