Businesses make money off of donations all of the time. For example, thrift stores take donated items and sell them at a low price for profit. A donation is simply a gift. When someone donates or gifts you something, there is nothing that prevents you from taking that item to a pawn shop or selling it on eBay. If people want money for their images, they should sell them.
Because donors can earmark their donations for specific uses, everyone who will handle a donation should have the same understanding about what they're allowed to do with the donation. For instance, did the donor grant Getty the right to license the images, and does "license" mean "sell"? Is Getty selling ownership rights to the donated images, where the donor no longer has any legal rights to the intellectual property? The resolution hinges on what the donor and Getty actually agreed to.
No, Getty Images is being greedy if it's selling images that were donated to them. Donated images should be made available to everyone for free. If Getty Images purchased rights to an image, they can resell those images at a higher price. But donated images fall under a different category and should not be sold.
Getty Images should not be allowed to sell donated images. Just because they want to make money on a photo doesn't mean it is ethical to do so. There should be rules set up between Getty and the donating party so that they get some kind of compensation or reward.