First of all, he is an alumnus of Cornell (singular, not plural).
Second- if he’s willing to write you a recommendation for ANY college which highlights your distinctive accomplishments, what a kind, ethical person you are, the contributions you make to class discussions, what a joy you are to teach- then terrific!!! But a letter from an alumnus doesn’t mean much if it’s just “I went to Cornell. He wants to go to Cornell. You should take him, he’s a good student”.
Third-Make sure you have enthusiastic recommenders, no matter where they want to college.
Good luck!