Sorry Ian, but it's not. You can use water resistant plasterboard, like Aqua Check, in wet areas. All wet areas have to be fully waterproofed now. This means the whole floor and (I think) 4" up the wall around the room and full height of the shower and any splashbacks.
Villaboard will give a very different paint finish to plaster. Not as smooth, sort of orange peel look. You also have problems with door jamb and window reveal thicknesses. On the other hand, villaboard will handle it better if your waterproofing membrane fails (you are installing one, aren't you?). It's a better substrate for tiles too.
"I don't practice what I preach because I'm not the kind of person I'm preaching to."