Depending on the size of the graduating class, Graduation may not be the best forum to announce scholarships. My d's class was over 600 and Graduation without extra announcements was long. There was only a reference to the valedictorian's college choice, and top 10% students were asked to briefly stand.
Her school always has a Senior Awards Night that announces: community service scholarship awards (i.e. Kiwanis, Rotary, etc.), top student in each subject (over 4 year period), scholarship awards, top 10%, NHS, etc. At this event ribbons/medallions, gold cords (top 10%), silver cords (250+ volunteer service hours), and a few other special medallions/ribbons are also awarded. My d was award a black/gold ribbon and medallion representing the Army (West Point) from the school's recruiter. The students are allowed to wear these ribbons/medallions to graduation. Her black and gold certainly stood out amongst all the red and gold (school colors). She was only 2 that went to SAs; the other went to AFA prep.
The sports teams have their own banquet celebrating all the achievements of the teams and team members, including sports scholarships.
Sometimes principals have a hard time breaking traditions, or with all their other duties, just choose not to take on one more thing. Maybe a committee of senior parents could volunteer to coordinate/assist the Guidance Dept.
Go for it!!! Good Luck!!!