Is it ethical to develop software for financial company?
I assume you're looking for an answer based on this definition:


  A lay follower should not engage in five types of business. Which five? Business in weapons, business in human beings, business in meat, business in intoxicants, and business in poison.


I'd guess so (that it is ethical or not inethical to develop software for a financial company).

Consider telecommunications or telephony software, for example: theoretically the internet and telephone system is also used for trading meat, but, that's not exactly your responsibility: the same is true for anything -- making cars, for example: a few cars, too, are used in the trade of meat.

I think I mostly just avoided employment with aerospace (i.e. defence, weapons) manufacturers.