I always thought they could explore (and by that I mean go walking around in duo in an area), but I believe you need to step out of duo at the explore points and look at things out of duo to get any benefit xp wise- which can often lead to you dying of course i.e. probably not wise to take on an ancient dragon solo just to try and get a little exp/obs xp for looking at him.

It may be that you need to enter the point out of duo and not pop out in the room too, but on that I have no idea since I don't really know how the system works. That said, transmuters still make a pretty good exploration class, up there with conjurers, paladins and the like.