Can I use fruit juice to take my Creatine while on the slow carb diet?

No: fruit juice breaks the "Don't consume fruit" and "don't drink calories" rules of slow carb.

Creatine is better utilized when taken with simple carbohydrates, you are correct, but I would think this could also be accomplished by taking the creatine before a meal, with which you consume veggies/beans that your system breaks down into simple carbs for your body to utilize.