Ah, well, zombie absorption is something I haven't seen before, so kudos for teaching this old dog some new tricks. I actually like the idea of Nurgle "eating up" the freshly dead, so to speak, and incorporating their soon to be diseased bodies into his already shambling horde. Man, almost makes me want to collect chaos now.
As for bolters, I think rust is the traditional way to go, you'll see most players take that route. What about making the weapon seem alive though, as if it were demonically possessed? Maybe paint some of them fleshy like your marines, with some pustules for fun? Or maybe have the flesh blend in and out of the metal, but make the metal grimy and blackened instead of rusted (or else you won't get much of a transition color-wise)? I don't know, just tossing out ideas.
Also, that would make your dad's a 4th gen, as the 5th are not out yet (to my knowledge, anyways). Basically, I have the same thing, minus the phone part, which makes me wonder what I'm doing wrong when it comes to trying to take pics with it. I'll fiddle around, see what I come up with.