Not exactly. RAS is Road Active Suspension as I understand it and 4th Gens didn't have it. I think what you mean is X-REAS ("Cross Linked Relative Absorber System").
This video explains it. As for the relative difficulty of lifting with X-REAS, any 4th Gen you buy with X-REAS is 99% certain to need it replaced. The refit cost with OEM parts (there are no aftermarket X-REAS components to my knowledge) is so ridiculous ($2K+) that everybody simply removes the X-REAS system - it's easy, see the suspension post linked in my sig - and installs standard suspension components. Bottom line is that I wouldn't worry about whether a truck has X-REAS. If the frame is relatively clean rust-wise, the 4WD is confirmed to work (frozen actuators from disuse is a known issue), and it's otherwise reasonably solid, go for it.
Happy to answer any other questions as best I can, whether X-REAS or whatever.