You're fine to run 'incorrect' offset wheels on the front and rear. Obviously, as you've noticed, you'll have to spacer the fronts out.
As for the rears, if they don't touch anything, (might be worth dropping a wheel off, dropping a spring out and undoing a shock, then putting the wheel on and lifting the wheel up to see if it touches the inner arch at all, if it does, is it anywhere near the point your suspension would travel to?).
Personally, I think they'll probably not look very good, unless they happen to be particularly wide dishy wheels (thinking 9J+ ET20 here), but they should be fine, if you want them, just chuck them on!
Out of interest, what wheels are they?