You can check the voltage from the stator directly to see if it is outputting anything. Unhook the harness from your stator and set your multimeter to AC voltage. Rev the quad up to around 4000 RPM and see what you have. I am not sure the specific voltage on the vipers though but that will tell you if the stator is doing anything.
Make sure you are set on AC voltage for this test, the stator outputs in AC, the regulator/rectifier converts that to DC and regulates the amount of voltage getting sent back to the battery.
I have a service manual on the Sierra DLX90, it's similar to the viper but it doesn't say anything about testing the charging system.
2008 Raptor 700SEII - 770 13:1 big bore kit, barker duels, webb 4 cam, p&p head
2006 Outlander 800 Max XT
2007 Honda 250EX
2000 Eton Sierra DLX90