Well, for the purposes of this boss fight, he's welcome to think it's his COMP doing the summoning, but as mentioned above, it'll really be the product of something a little more vague, and not actually the result of the machine.

As for the skills he can have, scanning the enemy for stats and skills won't do him much good in this fight, but he's welcome to have something similar to the Harmonizer — giving him (and the people around him within range) an increased resistance to the fatigue of being attacked, which in turn will let them fight longer.

So, the ability to summon demons and the ability to effectively buff the people around him to let them fight longer! Remember that if he uses both at the same time, he'll get weaker faster than if he were using one or the other separately, but have fun with it!