Yes, you can definitely enter VMMC for a tour.
It is a government owned institution, so you can visit the campus and have a look at its facilities. You can also catch a glimpse of AIIMS across the road from the Terrace Garden. But some areas like the library may be restricted for outsiders. You’ll require permission to enter classrooms and dissection halls.
You’ll love the green and beautiful campus of VMMC. It is especially mesmerizing in the evenings.