Hi Michael.
No, in my experience, Zi Fa Dong Gong is not riskier than other qigong exercises. When practiced correctly, it's very safe.
Exercises like Zhan Zhuang are much riskier because adding energy without first clearing blockages is akin to increasing the pressure of a clogged pipe. I know people who have hurt themselves practicing Zhan Zhuang incorrectly out of books, but I don't know anyone who has hurt himself practicing Zi Fa Dong Gong, either out of books or learned directly from a master.
On the other hand, it is possible to practice Zhan Zhuang as a mere physical exercise, which isn't building energy and therefore doesn't carry the same risks. The same is not really true of Zi Fa Dong Gong because, if you're not practicing it correctly, you won't have spontaneous movements.
