No, creationism is not itself a cult, at least not as the word is commonly used today. However, there are people who identify as YEC who do behave in a very cult like manner. The same could be said, however, about just about any theological viewpoint.
What concerns me about some YECs is that there is a bit of a conspiracy theory mentality that underlines this viewpoint for some of its proponents. This is the notion that the scientific community knows that the Earth is only several thousand years old, but promotes an old earth agenda to undermine Christianity or that there is a great treasure trove of anti old-earth evidence that is being systematically suppressed by the scientific establishment. These arguments are somewhat troubling to me because they seem to be built on the same type of manipulative tactics that many cults utilize. I would not say, however, that these tactics are, in any way, representative of YECs in general.