I can't speak about Nassarius snails, but I CAN say that the microhermits I had were a bunch of thugs...
They decimated my snail population...Nerites, gone...Trocus, gone...Strombus, gone...Limpets, mostly gone, but no babies in awhile...
The only survivors were those who stayed on the glass more than the rocks...
How do I know it was the hermits?
I put a dozen Bumblebees in the tank, by the second day there were 7 empty Bumblebee shells...
I got pissed and removed all the hermits...
All of the remaining 5 Bumblebees are stil l kickin' 2 months later...
No more hermits for me...