I guess if you want a special tank its decent. Id aim for an offensive set with Timid.Is a Calm HP Ice Nihilego worth keeping? I'm leaning towards resetting again, but I want to make sure.
IVs are 30/11/28/31/31/31
I wouldn't use Nihilego defensively. Rock/Poison is not great defensively, coupled by Nihilego's utter shit physical defense is no bueno for any defensive pokemon. The x4 weakness to Ground makes the frailty even worse. Any tickle of a random Earthquake will OHKO it. Stuff That Nihilego is supposed to check like Charizard-Y can simply run EQ to kill it.
You're choice though. The offensive suicide lead set with Sash seems to be the most practical.