Andrade says the Blizzard recording was "the most secretive thing I have ever done" -- they didn't show him anything visually about what the character was or did, and apparently he wasn't even allowed to take the script out of the recording room. Andrade also says that Blizzard is keen to let voice actors do their thing -- rather than giving direction, they let the actor come up with lots of their own reads, and then chose the one they wanted to use. It's almost hard to believe that Blizzard's voice acting is so good, given how hands-off they are (you'd think they'd aim to connect it with the art or animation in some way), but Blizzard fans know how well it works -- the voice characterisation in Blizzard games has always been terrific.
Very interesting -- while Blizzard's voices are one of the things that have really made their games successful, it's strange that they've never let us into the process more. Their sites are full of concept art and model designs, but it would be cool to hear an uncut recording session or find out exactly how voice recordings are integrated with the game. Maybe we'll see more on that in the future.