I've seen Dorn play 100 games or so and GOYA is right. He's poor defensively only because of speed. In an OF with Bruce and Stubbs, he's good enough, IMO. His defensive stats all grade out as average or just below. (In fact, his range factor for his career matches up fairly well not only across the minors, but on his team-- as a LF only, that is.)
IMO, he's better with the glove than Gomes, only because he's fundamentally sound. As stated earlier, he's not likely to throw over the cut-off man's head or to the wrong base. There's something to be said about that, after having watched the Reds for the past decade. (Though I do think they improved last season on that count by a great deal.)
I think Dorn's ceiling is what the Reds got out of Gomes last season with a slightly better glove.
Is he better then Dickerson on the corner? That's tough to figure out. Dickerson should be really, really good as a LF (though his lack of experience hurt both him and the Reds in a few games last season). He has power he didn't show last season (at all) as well. Dorn's power plays much better and his swing is better, IMO-- short, slight uppercut, balanced. I'll take the easy way out and say they're about the same.