If you ride slowly enough you get fair accuracy. The higher ur HA the less penalty you get for shooting ont the go. 0 for luck shotguning, 2 is the bare minumum, 4 is satisfactory. Remember tho that HA still requires 6 agil each. If you halt your horse while shooting you still shoot a bit less accurate then on foot IMO.
Throwers are more dangerous with thier uber lances torpedoes and rapid fire throwaxe, darts. 1 stray hit to the face and you can call it good night!