Leveraging private capital
Its legal to borrow and lend money, but if you become anything close to a bank, (take deposits, make loans, take risks, make a business out of it) then you will be regulated. You will be insured by the FDIC, and since you are insured, you will then be required to follow certain guidelines regarding how you asses risk and which risks you can take or not. Moreover, they will not be allowed to lose money in a large scale, so they would have to recapitalize the 'bank' after any of the charitable projects swallows up capital.

So to answer your question, they would not have more wealth, but they would manage a bigger pot of capital with which to invest. However, at some point they will lose the freedom of doing whatever they want. Since its not their money, then they can't do whatever they want.