Could Doran have been projecting the Golden Company with his numbers already? He's a sneaky guy. Maybe he's had something planned all along. I also think he may know that Aegon is a Blackfyre, if he is of course (which I think he is). Dorne never really seemed to like the Targs. It was sort of an uneasy peace between them. Doran seems like the type to go with whoever will help him win. I think in reality, he could care less if Aegon really is a Targ, as long as everyone else thinks he's a Targ.