In general, no. In fact, several graduate programs may offer TA/RA/ fellowship covering 9 months, so you would have to arrange something on-campus or off-campus for the summer. However, specific situations may differ. For example, I have a 12-month fellowship and am expected to work in my lab during the summer (which I want to anyway) but may take off for a week with my PI's blessings.
Many things in graduate school are by arrangement between the graduate student and the PI, and this likely applies to your question as well.