Photographing homeless people is very different from taking photos in the hood.
I actually went down to the hood in Raleigh today. About 5 exposures and 20 bucks later, here's the advice I can give.
1) Try to avoid wearing red or blue. Gangs will know that you're not a blood or a crypt, but it's still not a good idea.
2) Cash is your key in and out of the ghetto. Do not carry a wallet or cell phone with you. Carry your camera in a camera bag, a small amount of cash, and a pack of cigarettes and lighter, even if you don't smoke. 20 or 30 bucks is sufficient. When you walk into the ghetto on foot, people will assume that you're either a) A cop, or b) Trying to score.
3) Know how to deal with people in the ghetto. Almost all hookers have pimps, and you don't want to make them angry. Dope feinds will approach you, and will usually leave you alone if you give them a cigarette and a couple bucks to buy a beer.
4) There's a lot you can purchase. Drugs, information, and protection. You should probably know the drug lingo. Hardly anyone sells weed. Most people sell crack, some sell heroin or meth. In Raleigh, they refer to drugs by gender. If someone offers you "girl," that means they're selling crack. If they offer you "boy," that means heroin. People wearing red are, indeed, bloods, and people wearing blue are, indeed, crypts. Stay away from them. I hooked up with one of the nicer guys trying to make some money to score. For 15 bucks, he told me where and where not to go, and what and what not to do. He also let everyone know that I wasn't a cop, and that they shouldn't rob me. His biggest piece of advice: "Stay off the block." That means I can take photos of whatever I like, so long as I don't try to photograph anyone hustling (dealing) or pimping, and I don't try to photograph any gang members. His other piece of advice: "Don't talk with your hands."