I have tried adding Isopods to my eublaberus bin multiple times now. it seems that they do not survive the week. I have bark and leaves. Are they being eaten?
Maybe...I see the same thing in my enclosures. The roaches MAY also be out competing the isopods for food. My colonies are very dense and the roaches devour the food very quickly. I have seen a single adult kick a single large ground beetle (Genus Calosoma) out of the way just to eat a slice of apple. The roach will then eat its fill of the apple and then leave. Only then can the beetle eat from the apple. Or maybe the roaches are just eating the isopods. What Eublaberus species are you talking about? I have seen my Eublaberus posticus (Orange Head Roach) chock down on other smaller roaches.
Eublaberus are known to be aggressive to other inverts, I wouldn't be surprised if they kill and eat is isopods, I have isopods in lost if my copies but not in Eublaberus...