If you think that SIAI is the best charity, and you work for SIAI, should you give any money to charity?
The fact that you work for the SIAI does not change the payoffs much at all. If it would have been worthwhile donating to the SIAI if you did equivalent amount of work for Hewlett Packard and it was beneficial to donate to the SIAI then the same will still apply if you happen to work for the SIAI. (Crudely speaking at least.)
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.
But then you should instead donate to them by taking a pay cut, so they don't have to pay taxes on the money they give you that you give back to them.
But you've already taken a pay cut by working at SIAI! By this logic, and induction, anyone who works for the SIAI, should work full-time, for free.
If you think that SIAI is the best charity, and you work for SIAI, should you give any money to charity?