Kiva loans have a negative expected (financial) return with no possibility of making back your money in real terms - you cannot, by definition, "invest" in a Kiva loan. Kiva is a fun place to do some good. I do not think, however, that it is any kind of training for investing.
If you're running a successful startup and looking for some kind of charity outlet for some of those profits, I highly recommend Kiva loans. Find some entrepreneurs trying to start tough businesses in tough environments, like a tailor in Liberia or a corner shop in Congo, and loan them solid chunks of money (e.g. $500 at a time).
If they repay the loan (which the ones I loaned to have so far), then:
1) you've helped start a business in a deprived part of the world, possibly changed someone's life
2) you've got the money back to help another business
And in either case:
3) you've done something very tangible to help another entrepreneur who is dealing with business risks you are lucky to never need to consider in your entire entrepreneurial career.
With Kiva, you can lend money at 0% interest to a microfinance institute, which utilizes the interest-free capital to give a loan at a slightly lower interest rate than it otherwise would.