I realize how pedantic this is, but it’s a weird pet peeve of mine…Alumni is plural. If your teacher is male (and just one person), the word you want is alumnus.
And agree with the above - his alma mater is not as significant as what he is able and willing to say about YOU. If he knows you well and will say great things about how you’re the best student he’s had in the last ten years (or whatever stellar compliments may be appropriate), then great. If it’s more just, “Yeah, I had this student, he was fine, by the way I went to Cornell,” then no, that won’t help you at all.