Of course it helped their cause. The "helping their cause" is different from "being compensated." At best it is some kind of potential deferred compensation that is going to be paid by someone else, not their school.
During Manziel's senior season, A&M brought in $740 million in donations, which is $300 million more than any one-year period in the history of the school. It is impossible to gauge how much of that he was directly responsible for, but even if it is just a small fraction of it, does his scholarship even up the scales?