I've been on Rad melee a bit recently, and you can (and should) 6- slot Irradiated Ground with procs.
The reason is that IG is not a standard toggle damage aura, those check for proc trigger every 10 seconds. IG is instead a pseudo-pet, which spawns every 5 seconds. So, every 5 seconds, it checks for proc activation as if it were an activated power. This is set- defining, for me.
Go for 6 damage procs (if you include the purple PBAOE proc, you can get that many) or 2 -res procs and 4 damage procs. Solo, the latter might be the way to go, stacking that -res with Bio's.