Its original use was apparently in the British
theatre. I've seen it used
for those who fund political projects, for example, in referring to rock
stars such as Bono. In the case of actual investors in startups, a advice
component could certainly come into play. Financial return is not
essential to the concept however.
At any rate, I see no problem at all in calling our major financial
supporters "angels" (Well, not really, obviously there is a religious
connotation which might be inappropriate)
Yeah, it's close enough. I think "benefactors" is better, though.