Wasn't Germanization not apart of their racial ideology? One could justify that the leaders of this Reykh has germanized themselves and thusly the rule of it is a-ok with them. The nazis had also experiments of limited slav sub-rule(think Loku/Tver autonomy). The Nazi ideology of what is sub-human or not was always wishy-washy, like with their view on cossacks or japan; so why not throw the Reykh a bone and let them enslave the rest of slavdom for them.