Gokul Rajju Doaham is never good in horoscope matching. It is formed when certain Nakshatras are in the same group. Of course it is one of the many things that are important to check when doing horoscope matching. If you have Rajju dosha chances are there that you also have Nadi dosham. You need to check if these dosham get cancelled before doing marriage. You may read more about Rajju dosham from the link below.