It depends on the individual. For some it may help. Although, for others, like myself, it just makes it worse. I don't smoke weed anymore in teh first place, because all it does it induce a panic attack, raise my heart rate, and make me paranoid. Hell, it feels worse than any crack comedown I have had, lol.
My point is, if weed chills you out in the first place, it may help alleviate cocaine comedown symptoms. But for others it can have the opposite effect. So start with just a couple hits and see what direction it brings you. Don't just house a joint and then end up having a wicked panic attack. Personally, a small dose of a benzo or opiate is more ideal for cocaine comedowns.