Yes, tea is mostly water and your body breaks is down for utilization in a similar manner. Just keep in mind that caffeine is a very potent diuretic, therefore it will increase your urine output and cause for a need in water intake.
On another note, "8 glasses of water per day" is a complete sham, and has been for years. That was something the military said in the 50's, and it has since been debunked (many times over) Ideal water consumption is between 1/2 gallon and 1 gallon of water spread throughout the day. Your body needs water to function, and they more hydrated you are, the better your body functions, and in return, speeds up your metabolism.
Don't get so caught up in follow a meal plan verbatim. They are set there as guidelines to give you a track in which to follow. Fat Free Milk is a great additive to your coffee. Try mixing 2 cups coffee, 1/2 cup FF Milk and 2 scoops chocolate Whey into a shaker, mix, and enjoy!