I think it's pretty common knowledge that Hitler viewed the Slavs as subhuman or 'untermenschen'; however; his attitude towards the Slavs as regards the conquests in Eastern Europe seem somewhat haphazard: he made alliances with existing or newly-created Slavic states (Bulgaria, Croatia, Slovakia) whilst others were not even given even puppet-state status (Poland, Russia). Now; Nazi policy in some cases as regards the Slavs sometimes hand waved various groups as 'not being really Slav'; for example in the case of Bulgaria, mention was made of the Bulgarian's origins as a Turkic people who later became slavicised and adopted a Slavic language, and a similar origin story was posited for the Croats, and thus Hitler could . It's also certainly true that the Poles, and Russians were particularly low-down as regards the hierarchy as regards the Nazi's attitudes towards the Slavs: both groups were part of the Nazis' genocidal policies in the east and both were denied their own, even puppet state.
So we can divide the policy of Hitler and the Nazis as regards the Slavic peoples threefold:
Those that were treated on a equal footing with Nazi Germany (and explained away by them 'not really being Slavs'):
Those that were given puppet-state status:
- the Czechs
- the Serbs
and those that were not even given puppet state status and were to be exterminated and/or 'germanised':
I realise that a lot of this was practicality and realpolitik on the part of Hitler, but; given his racist attitude towards the Slavs, why he would be seemingly so 'accommodating' to the Slavs in this respect. I'm particularly interested as to why the second group weren't treated in the same way as the third group (Poles and Russians)