Kool Aid Ingredients (from WikiAnswers):
The "unsweetened" form of Kool Aid contains fruit flavoring, citric acid, calcium phosphate, salt and Vitamin C. Some flavors add maltodextrin if natural fruit solids are used.
The "sugar free" mixes add aspartame (Nutrasweet) and acesulfame potassium.
The "sugar sweetened" mix adds sugar, sodium citrate, and the preservative BHA.
Beyond the "obvious" problems of injecting such things as "fruit flavoring", "natural fruit solids", BHA and Acesulfame K... Na, this is a perfectly safe thing to do.