GIBS is pretty flexible when it comes to entrance exams. They accept almost all the common management tests — CAT, XAT, MAT, CMAT, ATMA, State CET, and even GMAT. In my batch itself, we had students who came through different exams, not just CAT.
Honestly, that's one thing I liked about GIBS — they don't restrict the admission chances to only one or two exams. If you've taken any recognised management entrance, it counts. After that, they focus more on your overall profile, interview, and how serious you are about management studies, which makes the process feel fair rather than purely score-driven.