Zulu, I've grown iris in irrigated beds with roses and perennials, and they all seem to play nicely together.
Pill bugs normally eat rotting, decomposing tissue, unless they're crowded and hungry, then they'll go after healthy tissue. But I wonder if you're looking at the mother rhizome? They'll lose their roots as the offshoots take hold.
I think in my garden, where I'm not as successful as I'd like, it's because I need more nutrients. I use a lot of wood chips, and the can rob the soil of nutrients. I'm going to be trying alfalfa pellets this year, or maybe some chicken manure.
