His use of the prosecutor's office to destroy a rival suggests otherwise. Abusing one's authority to get government agencies to provide you with details of a rival is corrupt.
Also I think BP is referring to the 2006 charges against Ma for using special funds for his own purposes. Chen admitted to using his, and while there actually was nothing illegal, is was not exactly ethical as he suggested
Ma on the other hand maintained he had every right to use the money as everyone considered such slush funds part of their salary. He was found not guilty, largely because there was no obvious intention of committing a crime, though oddly his secretary still had to do jail time.
My general contention is that people like Ma don't really need to be corrupt as the work of making them wealthy and connected was done by other people. I suppose it is still a good sign that he is not additionally venal but that is obviously faint praise.
Of course those close to him, such as the former finance minister, have escaped serious charges with minimal sentences. With nary a peep from Ma this does not look good.