No thinking atheist, including Dawkins, will tell you that there is absolutely zero chance that a god exists. What they believe is that the chance of a god existing is so incredibly low that they consider themselves atheist.
So you want to call Dawkins an agnostic because he might subjectively estimate the chance of there being a god at 0.000000000000001% probability? That's just being an ass. He's an athiest for all intents and purposes. The only reason he's saying there is any chance that there's a god at all is because he admits he's not omniscient.
I don't know much about hinduism, but he's probably ok with Buddism cause there's really no god or spirituality in it. It's more of a life-philosophy for living well. If you reminded him about reincarnation he'd probably be more against it. But I don't even know if Buddha himself believed in reincarnation or if idiots added it later. Either way, Dawkins is probably more against Abrahamic religions because of their virus-like nature of spreading by some type of force.