Do we actually make anything from this arrangement? I don't mean the amount they would pay, but the net profit after the costs involved are deducted - floodlights, utilities costs, any stewarding costs, etc. etc. I'd hazard a guess that the profit from hiring out Cappielow for this game would probably be very small. I could see the logic if we were actually making a significant sum, but I suspect it won't be worth the effort financially. That's before you consider the moral arguments as outlined by Toby above.
We haven't had to play any of these B teams so far, but eventually we might get drawn against one of them. If that happens, would we refuse to play them and just forfeit the match? Unlikely I think as we'd be cutting off our nose to spite our face. In practice the rules currently allow them to take part and we have to abide by the rules.