Should Ma Bo be considered a victim in the history of the cultural revolution?
First, let's consider the full title: Blood Red Sunset: A Memoir of the Cultural Revolution. We can assume, then, that this memoir is a true story of the author's actual experience and is about the cultural revolution in Mongolia. However, in answer to your question, there is no "right" answer. By nature, it is an "opinion question." The key words, of course, are "should" and "victim." Let's take a look at what the cultural revolution truly was in China and then allow you to decide for yourself.
The Cultural Revolution in China was a movement that was both social and political. It took place in the People's Republic of China from 1966 until 1976. Mao Zedong is responsible for the movement in order to keep Communism alive. Mao wanted to "purge" capitalism from Chinese society while bolstering his own ideology. It absolutely polarized the people and crippled both the economy and the social structures of China.
In my opinion, I don't think Ma Bo should be considered a "victim," because of his amazingly brave rebellion against the Cultural Revolution through his own text. Instead of calling him a "victim," I would call him a "survivor"! Ma Bo survived numerous betrayals from those who he thought were on his side. Ma Bo, of course, begins as one of the "comrades" who tried to convince teh capitalists to change their ways. Through this struggle, Ma Bo learns the humanity and the compassion of people who were supposed to be his "enemies." As a result, Ma Bo becomes completely disillusioned with the entire movement and eventually denounces it at completely wrong. Through his memoir he completely denounces the Cultural Revolution and explains his reasoning for emigrating to the United States as a young Chinese intellectual.
Further, I have personal experience with those who escaped the Cultural Revolution through a professor of mine who taught me Chinese Literature at Furman University in the 1990s. This professor always told us a story about how happy he was every morning to wake up to the sound of an alarm clock because it meant him escaping the confines of Communism during that Cultural Revolution. Before he escaped from China, he was always roused by Mao's voice, instructing him on what should be done at precisely every moment of the day. Who would have ever thought an alarm clock could be the cause of such joy! Just like my professor, Ma Bo isn't a "victim," but both a revolutionary and a survivor!