Answer

I do not have clear information about this foundation. My impression is that it does not have immediate missionary goals, but in the background of the donations there is an evangelical outlook that one should support and preserve the Jews (and keep them as Jews) because in the end of days they will "return," meaning they will convert to Christianity. Therefore it is hard to say that there is a halakhic prohibition here, especially since I am not giving money to needy people who require it in place of the foundation's money. I cannot forbid this as a matter of Jewish law, but it seems to me that it is proper to avoid it as much as possible.