Yeah, you can definitely get a scholarship based on MAT score for PGDM at GIBS. In fact, in my batch quite a few students came in through MAT and got some level of scholarship depending on their percentile and overall profile. It's not like only CAT matters — MAT is also considered seriously along with academics, personal interview, and sometimes extracurricular stuff.
What I liked is GIBS doesn't make it feel out of reach. If your MAT score is decent and you perform well during the admission process, there's a genuine chance. So yeah, as a student I'd say it's totally possible and worth trying instead of assuming it's only for top ra