In that case, I would probably go with no. There's no reason a dragon can't blast from any of its squares - I mean, there's no "facing" - so the only reason they would want to include themselves in an attack is to shoot in such a way as to hit PCs on two sides of them; for example, left side and behind (and possibly right, too, depending on the size of the dragon and the blast). And because that's a bit too ...something (powerful?), and because it doesn't seem to follow the spirit of the rules, I wouldn't do it.
Dragons are tough enough without blasts that can hit everyone on three sides of them. Besides, that's working into "burst" territory.
Now, area effects - sure, that's no problem.