No personal experience, but I have read many times that it is only for couples to share and join in together.
It is not true that both spouses must participate in the telephone coaching service, if that is what the original poster meant by "counselling".
There are 3 ways of getting MB coaching direct from the Harleys:
1. You can write to Dr Harley at the radio show, and he will answer your email, including follow-up questions. It is common for only one spouse to seek help, and the participation of the other spouse is not required (although, obviously, it would be ideal). Dr Harley's wife Joyce invites some of the people who have written in to speak to them on the radio show, but you do not have to do this, and you will still get help from Dr Harley. Dr Harley is always keen to hear from the reluctant spouse, and he and Joyce will encourage you to seek their participation, but this often does not happen, and help is still effective. This is free.
Many people write to Dr Harley with no intention of going of the show, and he answers their questions without reading the email on the show. This, as I said, is free, and does not require the other spouse to participate.
2. You can pay for telephone coaching with one of Dr Harley's children, who run the telephone service; his daughter Dr Jennifer Chalmers, or his son Steve Harley. You cannot speak to Dr Harley himself via this method. Again, it is common for only one spouse to use this service. The whole point is that they are often trying to get help with a withdrawn spouse, who by definition is not interested in working on the marriage. Jennifer and Steve will usually make suggestions to get the other spouse on board, but they will coach one spouse for as long as necessary. The service is expensive, at about $200 per hour, but it is designed to change behaviour and be effective on the marriage as quickly as possible - hence its description as "coaching" and not "counselling". The goal is not to talk for years on end, but to act, quickly, on the marriage.
3. Finally there is the online course. This is the Home Study course, which is designed for couples to do by themselves (and which costs very little), but with the online version, the couple is assigned a coach who is trained and closely supervised by Dr Harley. The couple completes lessons from the Home Study course (e.g they work on eliminating a specific love buster that they identified as a problem, they report on their progress to each other and the coach, and when the problem is eliminated they move on to the next lesson). The online course costs about $1000 and is designed to take one year to complete. The couple is sent a wealth of Dr Harley's books, CDs and questionnaires as part of the package, and they are given lifelong access to the private forum on this site, where they can post questions directly to Dr Harley. While they are completing the course, they have access to their coach by telephone (as well as email).
The online course is the only coaching that must be done by both spouses. One spouse should not attempt to sign up to the course if they have an uninterested spouse who will not participate.