At this link:
Moto Q Flashlight | CharltonFamily.net
you can find another example (and source code) for activating the Flash light. Although it's for Moto Q, the documentation says it might work on other Windows Mobile devices as well.
The source code includes the code for the native-library (however, on the page you may find the library already compiled) but more importantly, it includes a wrapper for this library in C#.
I have no device with a Flash so I can't test. Don't blame me if it doesn't work, if it ruins your device or if you need to make a hard-reset.
Good luck.