The current version of Max (and previous versions) shared the angle snap between the modeller and the UVW editor.
The angle snap is usually on or off when it isn't needed in the UVW editor.
You can't easily assign keypresses if you already have S or A assigned to Snap/Angle Snap (as I do), as the UVW Editor has S and A assigned to flip element X and Y, unless you select over-ride which is so tiresome after a while.
I think the UVW Editor should have it's own angle snap, and not dependent on the main toolbar button.