Hi Shudha,
We have a slightly different take on it. In theory, yes, it should not matter whether you submit a GRE score or GMAT score to ISB. However, this is the
very first year that they are accepting GRE score.. uncharted territory still.
Most people who apply to ISB for the 2017 intake are still likely to take GMAT and not the GRE. To add to it, it is not really the norm to add up the GRE Quant and Verbal reasoning scores, so you have two numbers in your GRE score. Contrast it with the GMAT - a nice solid number that B-Schools can trust. A number that is used by ranking systems to rank the MBA programs. A number that can be marketed easily. It is hard to go wrong!
Besides, the GRE and GMAT percentiles don't have an accurate standard correlation because the population taking the GRE is typically college students while the population taking the GMAT is experienced professionals.
Of course, ISB, like all other colleges accepting GMAT and GRE scores, will have its system of comparison.
But just to be on the safer side, we'd advocate waiting for one application season before going the GRE way.