Is Coke Zero as bad as Diet Coke?...as in terms of diabetes-wise?

Good answers already.   Soda is part of why you have type 2.

All soda, is meant to be an occasional treat, rather than your main source of fluid, diabetes or not.

What matters in your diet is lowering you daily/per meal/snack carbohydrate consumption, refined simply carbs, to complex whole food carbs. 

What you eat and drink, is going to depend on how proactive you are going to be, WITH YOUR diabetes. If that means you are happy with high A1c's and higher than 200 blood glucose levels, pre and post meals, then that's a choice you make. 

If you like Coke 0 over Diet Coke, drink it. Just drink more water than soda, no matter which one you pick. 

Drink water. It's healthier.  You could opt for flavored waters, like LaCroix.