For the standard cell libraries (e.g. the 7t), it says that they are 5V, but the "Dualgate" layer is used over all devices which supposedly makes them 6V with the added oxide. Is this an oversite?

The base oxide is 3.3V; the thick oxide is either 5V or 6V, which is a process option choice.

Got it. Thanks @Tim Edwards

But that's something I need to investigate, as there is a 5V ID layer on top of the SRAM, so I'm not sure if that means it's possible to get both 5V and 6V on the same chip.