During college years, two of my close friends were roommates with each other and hanged out a lot with them. Both of them had gone through recruitment together and joined different NPC sororities, yet they still remained close friends. It was through their influence and encouragement that I first went to the interest group meetings when Theta came to my campus. To this day, we still joke that one of them is my Panhellenic big sister and the other my aunt!
In my experience, at most campuses, Greeks are friendly with one another. They support each other in Philanthropy and fund raising events. While there may be slight rivalries during times of recruitment, most sorority girls I know had friends in all the different sororities on campus.