Depends which Diablo you are talking about. But in general the stiffer a boot is, the thinner and stiffer the liner, and the more your leg fills up the cuff volume; the more effective the cuff alignment adjustment is.
From my experience with Diablo Race Pros the adjustment is very effective.
If you're talking about the dual pivot cuff alignment, I've seen it work great on some folks with funky bow-legs. It works in two ways - one to align the cuff with the skier's leg and two, to change the direction the cuff flexes, to help facilitate edge change.
The Tecnica race diablo has a different system for cuff alignment.