I wouldn’t be surprised if they exfiltrated enough from FireEye to make it worth it. It’s another premier security solution used by a larger number of highly likely targets. It will be interesting to se what FireEye vulnerabilities we see come out in the near to long term future. What kind of vulnerabilities can you find if you have the device source code?
Especially because FireEye doesn't have anything intrinsically valuable. Spend the time and/or money to buy/develop the security tools and holes FireEye has - or some equivalent.