Hah, thankfully someone finally got my Monkey King joke. You know, I asked for an animation of Roehm doing the whole whistle for a cloud when he summoned his cloud and everyone on the team (read: Americans) said they had no idea what Monkey was so it wasn't done.
Anyway, no you can't get past 50 on sneaking or thievery if you're not the rogue. Not all the achievements are available on a single run through!