mdovey - you're probably right!
But there's also another good reason to avoid a situation like this; if my wife had got the job and then turned out to be rubbish at it then it would have put her direct manager in a very difficult position...
I certainly think there's no justification for employing your spouse's firm to do work for your Charity. There's the possibility of collusion in setting the price, at the very least.
I suspect that if I had done something like that without my trustees' knowledge then I would be facing a serious "gross misconduct" disciplinary process. Ans if I HAD asked them, I think it would have a very short conversation (mostly about my judgement) and a resounding "no".