Dear MBALA2009,
An alumni recommendation is always helpful as they know the program best and can give insight into whether you will do well in the program. As with any recommendation, it is important the person know you for more than a year and have worked with you in a professional capacity or in a community activity. If the person is a relative or friend, it is probably not given as much weight and you would be better served by the alumnus emailing the Admissions Director a brief note offering support of your candidacy. Some schools have specific avenues for alumni recommendations, so you might also check with the school to determine the process, if any.
Regards,
Lisa