I've been punching my summoned attronaches until they turn hostile before practicing my destruction but is it necessary?

Are you asking if you can level up your skills, using your conjurated creatures as punching bags?,

Pff you can level up destruction magic in Skyrim even burning people with a torch xD, BUT Yes, you can level up with your conjurated minions. The best is the Ash Guardian without heart-stones in your inventory, it will always be aggressive to you right away and works like a placing a turret, it can not move from where you place it(Im 70% sure?). But they are tough and can kill you easily at low level.

REALLY if you dont have the Dragonborn DLC, or want something easy. Just buy a good old horse and use it as punching bag, wait and hour to replenish his health and your magic, continue until satisfied, you can even cast soul trap on this noble creatures and they will not turn hostile--> Animal cruelty for the WIN! xD.

As long as you do damage, you'll get skill experience. So the only time you wouldn't get any skill experience would be if you have the Companion's Insight ability from the Dragonborn DLC.