User blog comment:Bobbs3k/Can Ichigo's New Bankai be stolen?/@comment-11051098-20130630193625

I'm not sure they can steal it.

As stated by Nimaiya, Hollow Ichigo which has traces of the experimental Hollow/early Arrancar White in him, is Ichigo's Zanpakutô. He's part Hollow. Judging from the information we have about Hollow Ichigo's origins and race, Zangetsu is based on a part Shinigami/part Hollow being, which Ichigo is.

Judging from that, I think the Stern Ritter will still be unable to steal it, or at least have trouble stealing and accessing it's power.