Joey, I do a
lot of street shooting. However, I can count on one hand the shots I have of homeless people over the last 30 years. Why? Because they are easy prey and are constantly being exploited. You need to have a real empathy for your subject and shoot with what I call a
compassionate camera. If you really want to document what it is like to be homeless then you have to really dig deep inside and ask yourself- "why am I doing this."
It is easy to point a camera and snap away at folks who may be less fortunate than you. It is much harder to use that same camera and try to really document what it is like to be homeless. So what I am trying to say is- what are your true motivations for wanting to do this? This is not meant as a put-down on you, but put yourself in their shoes. How would you feel about someone who just casually started snapping photos of you when you are obviously in dire straits? As Stella said, everyone deserves respect. There is a wrong way and a right way to approach this type of photography.
Once again, just put yourself in their shoes and walk around a bit. If you do that, then you will understand their plight just a little better and it will make you a better photographer and will definitely make you a better person in the long run. Good luck to you in whatever you decide to do.