Don't suppose you're wearing a Powder Ganger outfit? Outfits affect how people see you, sometimes you can fool most people into thinking you're one of them, sometimes guards and such will see through your disguise and attack.
No, definitely not. That was the first thing I checked. In general, it seems like those Powder Gangers between Goodspring and the Mojave Outpost will attack me on sight, those in the NCR CF and surrounding areas won't. My status remains hated, but there seems to be little consequence to it.
If I'm hated, I assume they should attack. If someone can confirm this I'll just attack them myself and maintain the integrity of the game that way.