Quick Question: If I’m applying to X university, would a rec letter from an alumnus of that university be considered more carefully than a rec letter from a non-alumnus of that university, assuming the content of each is similar?

Quick Answer: If they are both solid recommenders, then go with the alumnus. Keep in mind that your recommender cannot be a friend or family member, and should be someone who has worked closely with you, knows your strengths and weaknesses, can comment on your character and work ethic, and can give solid examples of all of the above.