I'm not expert, but I'll state what's I know.
Of course halal meat will have blood uncooked. Any meat does. As for roasted chicken, the degree of the cooking doesn't constitute the way the meat is considered halal or not.
Besides the humane part of slaughtering the animal, the benefits from slaughtering in this way compared to let's say electicution, is that scientifically, the animal spreads in his moment of panic enzymes/hormones that are bad for human consumption. Blood also escapes the body of the terrified animal, usually results in less tenderness of the meat.
Semi-related information: Halal is an Arabic word, literally translates to "permitted" (contextually, permitted by god) that is synonymous with Islam. Judaism have more or less the same procedure (not sure if there is a single difference, but at the very least it's very similar). It's called Kosher