yes, gammarus are scuds.. i have bunches in my crayfish tanks.. they quickly dissappear when i grow minnows in the tanks, but after harvesting the minnows, the scuds manage to make a comeback, probably from hiding in the gravel
if you have a filter with media, scuds and worms will live quite well together, even totally submerged..
i set up a couple of bucket filters (filled with "scrubbie" pads with an airstone on the bottom) on my first system, when i moved things around and took the filters apart, they were loaded with scuds and red wiggler worms..