I don’t know whether Gu Kalai hired a body double or not (although there’s some online speculation in China over that question), and I don’t know about the use of body doubles in general. But it is possible (although illegal) for perpetrators of crimes to attempt avoidance of punishment by finding someone else to take the blame for the illegal act. There’s a term for this in Chinese (dingzui - 顶罪), which means to take the blame for someone else’s crime (or other action).
Here’s a short article (in Chinese) on the website China Law Info (a site established by Peking University in association with its Legal Information Center) about the practice with relation to traffic accidents. It’s written by a member of a country level judicial committee of the People’s Court.
The fact that this issue comes up sometimes in legal journals (you can find other articles on the issue by searching for 顶罪) suggests that i) people try this on, ii) the judiciary is at least sometimes aware that they do so, and iii) the courts are seeking ways to deal with it (e.g., the charges that should be brought against both parties involved in this illegal act).
