I'd say that the slann cast the spell, which did the wound. So in the end the slann still inflicted the wound, so I'd count Bane Head as working...
Also, just to mention, you can't take the Plaque and Rod of Storms on same priest as they are both arcane items...
So, I'm new to the forum and I'll be reading stuff and posting when I think I can offer some advice. I'm new to the 7th edition lizardmen,...