Right, here's where I stick my neck on the line. Personally I wouldn't worry about 2mm difference, in the grand scheme of things it only works out at 1mm per side, which could be a lot worse. Providing the bolt holes have been slightly reprofiled to suit you shouldn't have any major problem or safety issues.
The common issue with people fitting wrong PCD wheels and having accidents are usually two fold;
1) They try to get an extra 2+mm per side, which is when you start getting dodgy.
2) They fit a wheel with a close enough PCD (i.e. as in this case), but with a centre bore that's way different from the original wheel.
As far as I'm aware the Vauxhall centre bore and VW centre bore are pretty much the same.
At the end of the day though it's not recommended to fit wheels to a vehicle they weren't designed for, but it could be a lot worse. If you want to guarantee you won't have any issues though you'd be recommended to change back to a VW wheel.
Let the shooting down of me commence. :lol: