Can't see why not 🙂 I think green tea is supposed to be beneficial to health, although I really don't like the taste. It shouldn't affect your levels.
Apart from possible health benefits, I think it is a matter of personal tatse. If you like it, it wont do any harm and counts as fluid, we all need plenty of fluids. If it is something you enjoy it is doing you good any way.
I think that's where I stand on this too.
My personal favorite is lemon green tea. I have it without any milk or sugar/sweetener.
Its good to have some variety - no alcohol or fizzy drinks or fruit juice - so I've found green tea makes a change from tea, coffee, or water....