those nano-reef people have no respect for livestock I tell ya. As far as the origional question goes only small polyps and maybe one or two small snails or hermits. but evaporation would be a major problem.
There is a fish in there, its not getting the respect it deserves, there are even nanoreefers who put tangs in 15 gallon tanks. I'll bet a snail or hermit could live comfortably in a picoreef of 1 gallon however. What exactly is it that you differ on?