At points he doesn't sound dubbed...
I'm watching it right now and despite all the talk of Sam Jones being dubbed by another actor, there are a few scenes so far where they definitely use on-set audio of him (particularly in Zarkoff's lab and in the shuttle) and frankly his voice is indistinguishable from the ADR...
Is there any official credence to the idea he was dubbed. On re-watch, it seems like ADR (automatic dialogue replacement) is prevalent through much of the production, and not just for Sam Jones.