IAWYC, except there's one bit I'm not sure about.
Incidentally, to the extent that your income from the SIAI is equal to what you could be getting for the same effort elsewhere actually working for the SIAI is not altruistic at all.
If he is able to do useful work for SIAI that not many others can do, it would be better for him to work there and donate than to work elsewhere and donate the same amount. Yes?
If you think that SIAI is the best charity, and you work for SIAI, should you give any money to charity?