Our school’s College counseling office has a process for “outside” non-teacher letters, for the schools that allow it. There is a system in place for that recommender to confidentially submit the LOR to GC and GC then submits it to the schools that allow, or uses short quotes from it in their own letter. It is just a standard part of the process, typically used if a student has extensive and long relationship w the recommender which can add to the full picture of who the kid is , etc.