So I know several that do not feed pellets. They stick to lots of fruits, veggies, sprouts, nuts, seeds etc. My own personal is to give pellets with everything I just listed and even more.
Just to add, a reason a person is a vegetarian could be to several reasons an "ethical", health, religious or just aversion to meat. A cousin became vegan due to a medical condition, my boss refused to eat any meat starting at 2 years old so hers is an aversion, another loves meat but wont eat because of "ethical" reasons.