Jeff,
I just tried this myself on Windows 10 and it worked.
I brought up the Windows Task Manager, asked for "More Details" so the the PID would show, then tried SYS(nnn) with a number of the PIDs. It always seemed to return 0 when the process existed and -1 if it didn't.
If that is not working for you, let us know what version of Windows are you using in case Microsoft has changed something.