Cannot imagine how I missed seeing this thread, and your important question--which seemingly never received an on-target answer. At this late date....
To restate your question:
Aside from blaspheming the Holy Spirit (the "unpardonable sin", Mt.12, Mk.3, Lk.12), the short answer is "No". Whether Hitler himself crossed that line, only God knows.
The key is understanding that "all have sinned" (Ro.3:23). Indeed, Jesus convicted all of us as serial murderers (just like ol' Adolf) when he equated anger with murder (Mt.5:21-22). Yet Jesus intervened and paid for all those murders, and all other sin, at Calvary.
Remarkably, Scripture provides us with a Hitler-like example of a national leader who murdered millions but later was redeemed: Nebuchadnezzar. It took seven years of insanity to effect his repentance, but the Holy Spirit can do that. I doubt He did it for Hitler, but that's the game: more enter hell than heaven.
Thanks