Technically speaking, that's only 99% right. I was ROTC, and I have the GI Bill. This is because I was stupid enough to go College Program.
I haven't done anything with my entitlement yet simply because I haven't had the time. And from doing some light poking around many years ago, it did seem like the guidelines on what they would pay for and what they wouldn't pay for were pretty vague. Not sure what they say nowadays. I vaguely remember reading that they would pay up to a commercial ticket, so I always figured that if I couldn't find anything else, then I'd happily blow it on that. But to answer your question, yes, it should help pay for graduate work, up to a certain amount. However, the website only mentions 'college,' which simply means that all you have to do is call their handy 1 888 number to get a straight answer from them.