I believe the answer you’ll get from MU financial aid office will match what @guyk27 shared. While outside scholarships will not reduce what Miami offers a student for their MU Merit Awards, those scholarships likely reduce any MU grant aid that goes toward closing the gap between your EFC and MU’s COA. Likewise, MU’s Merit Awards would likely reduce MU grant aid as opposed to being offered in addition to it. After you find out from MU, could you post the official answer?
https://miamioh.edu/admission/finaid/contact-us.html