Okay, I'm in on the other side. In a situation where both sub and dom are novices, I think it completely reasonable that the sub might be trained by a more experienced dom, then returned to train in turn their dom.

Alternatively, the two novices could be trained simultaneously, but I do think the dom should be trained by a sub. If you were a quarterback (American football), wouldn't it be better to be trained by a receiver than by another quarterback? Or a pitcher trained by a catcher? You have to learn how to please the one you're going to be interacting with more than you have to learn how to please your peers. (And remember, relevant to this, that there's a difference between being trained and exchanging tips.)