I've only looked at the lib briefly but using an edge traverser, graba vector from each of the first 2 edges, do a cross product on them and you have the normal of the face.
Basically, the cross product of any 2 vectors gives you a vector perpendicular to the plane created by the 2 vec's. This may vary on the 'winding' of the face edges though, as I'm assuming the traverser follows the winding of the edges it should be giving you a normal pointing away from the face (to the outside of the solid).
Just had a quick peek at the doc's, you're right, no normal!? Even if you get the face's surface.
I noticed that there are point on face etc methods so it must be there somewhere, just not exposed.
I's easy enough to get though using 2 edges of the face you want.
hth