Anger can be a good moral motivation for the following reasons:
(1.)You are able to find a reason to your anger and gain experience.
(2.)You can learn through experience and time.
(3.)When you practice controlling your anger and your behavior in certain situations, you form habits.
(4.) Habits make for moral excellence.
(5.) You praise those who control their emotions and are good-tempered.
(1.) You shouldnt attempt to control something that can so easily consume you entirely, some things are not meant to be used as tools.(100.1.1)
(2.) You only have control over yourself as long as you can shut off negative emotions that could influence your decision making ability.(101.1.2)
(3.) It is in your best interest to avoid the very kindling of anger,, to beat back your negative emotions so that they do not plant the seed that will grow inside until it makes the decisions for you.(101.2.1)
Therefore, you cannot use anger as a tool to accomplish things. It is not something that is within your control, and by trying to control it, it will only further control you.
You can analyze what makes you angry and you can control it because if you realize how you feel when you are angry, who you are angry with, and where you started to draw the line. It can be good for motivation for yourself because if your loved ones are in trouble or hurt by another, you can use anger to come to their aid, protect them and punish them.
Anger itself is an emotion, and an emotion defined by aristotle's standards is any feeling that can effect one's judgement, attended by pain or pleasure. By aristotle's statement in itself, Anger is an emotion and therfore effects your decision by deffinition. If it effects your decision making capability then it is therefore out of your control. Your arguement is invalid because if you use something such as "anger", which is an emotion and out of your control, then the conclusion of the decision you make in any given situation is effected by anger, which means in some degree you are not making an unbiased decision, and anger is gravitating you in either direction.
If you do not have anger, you are, according to aristotle, "deficient" and you will fear everything and become a coward. However, if you are in "excess" of anger, you become reckless and are not afraid of anything. The good tempered person is in between these two and they do not give into their temptations. The anger in a person can meet in the middle and make one motivated to become a good-tempered person.
If we were to follow your model and allow anger into the decision making process, and according to your standards your anger level should fall perfectly between "deficient" and "in excess", then it indeed does not influence your decision in either direction. The absolute zero level of having no anger influencing your decision either direction would fit perfectly between "Deficient" and "In excess", and would not motivate you in either direction, which would actually help my arguement.