Buddhism is a legitimate school of religious thought, but it can seem difficult to approach. The point of Ole Nydal's approach is to reach out to people who do not have the time nor energy to seek out knowledge of Buddhism from various and assorted Buddhist sources. In a sense it's "bullet-point based" Buddhism.
I feel that Ole Nydal's Diamond Way Buddhism is a legitimate subset of historical Buddhism. Any branch or subset of a religion is important to the history of that religion. These subsets help form and mold the ways of traditional religion and become very important to the history over time.
I believe Ole Nydal's Diamond Way Buddhism is a legitimate subset of historical Buddhism. These centers teach about Buddhism and have meditation classes. They bring Buddhism to the western world and it should be considered a viable sect of Buddhism. Buddhism has many, many sects just as Christianity has many different denominations.
I do not believe that Ole Nydal's Diamond Way of Buddhism is a legit subset of the religion of Buddhism. I think that there are way too many people that are willing to create religions such as these and try to pass it off as part of the original belief.
The Ole Nydal's Diamond Way Buddhism is not a legitimate subset of historical Buddhism. True practitioners of Buddhism would not like the Diamond Way. It was just set up as a way to have people look at a really bad way of Buddhism and is a disgrace to the religion.