I wager that poor people are far better at recognizing addiction than non-poor. I hired a stoner once, not recognizing it. He robbed the company blind to pay his dealer.
Social workers are always trying to get the homeless addicts into rehab. They generally refuse to. It is their choice, not lack of money. In fact, I suspect that the lack of money is caused by their choice to be addicted. After all, addicts lose interest in their jobs and employers don't want stoners and drunks coming to work.