Is it a known technique to serve hot crispy-crust sandwiches on edge?
I think this is a perfectly legitimate question. Flat plating of a grilled sandwich will almost always result in the bottom piece of bread being steamed by the time it is eaten. Grilling with thicker or denser bread somewhat alleviates the problem, as well as grilling with a roll sliced and grilled on the cut side. 

As for presentation, your method is definitely not unheard of. The comment about the Club Sandwich is point on. You might also consider serving your sandwich with one half of the sandwich laying against some chips or veggie slices (carrot or celery sticks). That would keep the steam from developing under the sandwich. Then place the second half on the plate, barely overlapping the first. Grilled sandwiches are just one of those things that don't hold too long for service.