Yes Gatorade or any other non caffeine drink is good for you when you're sick to keep you hydrated.
I keep Gatorade around and stock up on the Gatorade when I'm sure that I'm gonna come down with a cold or the flu and it keeps me hydrated and makes me feel better.
Pedialyte is also good for you when you're sick with the flu to help replace lost electrolytes and it also keeps you hydrated.