Correct, that configuration should silently monitor whatever devices you have configured to trigger. You may want to double check that the client system you are testing with has the correct policy/policy revision and that the device you are testing with meets the criteria for the rule. If you enable debug logging it will also report exactly how DLP is seeing the device and what reaction it is taking based on the policy it is enforcing locally. Logs are here if you are not familiar with them:
I think I am observing the same issue/behavior - did you find out a resolution or any further information on this ?
My issue turned out to be a Device Definition issue that I am opening an SR about - Device Rule containing a Device Definition defined by Property “USB (VID/PID Codes)” with VID and Description defined, but PID not defined - causes DLPe to crash and Device Control doesn't work until the watchdog service restarts DLPe.