You would have to ask specific groups about their policies.
However, in general, it seems reasonable that a married couple might have more experience with the topic of marriage than a single person (unless it is a single person who was married for a long time and widowed, for example).
Of course, this is not always true, since a single person with a strong understanding of psychology and character, or who understands what makes two people compatible or incompatible, might also offer good suggestions for marriage.
Also, the presence of a married couple might hopefully cut down on one of the main pitfalls in matchmaking, and that is when the matchmaker decides to get personally involved with the client in a way that is not in their best interest and which is ethically inappropriate. (For instance, a man decides he should act as a guardian of an unrelated female in marriage matters, then he uses that authority dynamic to pursue a relationship with her.)
Still, there isn't any specification about this and if anyone, single or married, can successfully help two compatible people get married, inshallah they would enjoy divine reward.