I don't know about the international development side of things, but I do know about the nonprofit and public admin side. And yes, in those areas, being a gay latino would help you, because these are minority groups currently underrepresented in a field dedicated to the service of a diverse population. Also, there are funding opportunities that your minority status makes you eligible for. Coming with this kind of funding (or being able to apply for it later on) might give you a slight boost.
This might not necessarily belong in your SoP, though. You can mark off your ethnicity elsewhere on the application. If you're applying for a scholarship aimed at LGBT people, there would be a section to include this also. I know one friend waited until her interview and made sure to ask about queer life on campus-- she had done her research, and knew it would behoove her to mention that she was queer (in a subtle way).
If it's directly relevant to your motivations for applying, though, by all means include it in your SoP.