There is no getting around it Buddhism takes Karma from Hinduism as a fundamental concept because if it did not Nirvana, the escape from Karma would not be definable. Yet because Buddhism settles on emptiness as the escape mechanism then there is a fundamental conflict between these concepts that took centuries to resolve. Best example of a resolution is found in the Awakening of Faith. However, if you undertand that Karma is really an image of the Emergent Meta-system, how things arise, interact, are viewed, and then are annihilated in nature and in consciousness, then it becomes clearer why Karma is so necessary because it is the natural cycle of existence from seeds, to leaves, to flowers, to fruits. Also it is a relaxation process that moves from high to low energy, and thus seeks the middle way of optimization automatically as a natural process, like water flowing to the lowest point, or bubbles giving the smallest possible surface area automatically. So in a sense Karma is just this law of optimization in nature. Recently that as been named constructal law by Adrian Bejan Seehttp://en.wikipedia.org/wiki/Con….
Basically you are being asked to confront the fact that your self appears to persist even though the “truth” from the Buddhist point of view is that it is empty. Karma is the cycle that supports that apparent persistence. The persisence when thought of as perdurance is based on Being in the Indo-European tradition. Buddhism is basically asking us to return to awareness of existence from our immersion as a culture in Being.
What is fascinating is that whereas Being is the construction of an illusory continuity, Knowledge naturally has this persistence as part of its nature. So one aspect of Buddhism is to develop prajna, the wisdom of seeing existence in terms of knowledge rather than Being.
DzogChen because it is a heresy of Buddhism actually erases the distinction between emptiness and karma, and the distinction between emptiness in consciousness and void in nature. And thus this form of Buddhism does not necessitate the belief in Karma as an ultimate pre-requisite, but in order to understand that you have to go through Buddhism, so really is a necessity for DzogChen as well.