For your husband to be flattered is not really an issue. Anyone who gets a compliment is usually flattered.
But think of this in a female perspective. If you were driving a client in a car and got a compliment about how nice your legs looked, first thing to come to my mind is this guy a creep, as any female probably would. I would say thanks but be on my guard cause most creeps I run into start of with a compliment. Your husband can take the compliment as flattering but since he now portrays himself as a woman he must also have the instincts of a woman.
Edit: I just re-read where your husband drives at night. The night time makes one need to be especially cautious.