I'm also interested in this question. I'm looking only at Bryn Mawr and Goucher, and in looking at their applications, BM specifically asks for the SAT or ACT and then has an "Other" category, while Goucher asks for the SAT, ACT or GRE. My SAT score is now over 10 years old (though I scored very well). Would this be sufficient for both programs, or is there a time limit on the scores? I took the GMAT a little over a year ago (in b-school now) and scored in the 99th percentile overall, which in my mind helps to validate my SAT score. Just not sure how the schools will view it. And while I agree with your point that schools have no way to evaluate the GMAT, I would think the overall percentile should be relatively helpful in understanding it, particularly in this case. It also doesn't take much digging to find that the GRE and GMAT don't vary substantially in difficultly (consensus seems to be that GMAT math is harder while GRE verbal is harder).
Obviously will run it by both programs before I apply.