That sounds like a good way to do this. A simple trend log of the setpoint and the shadow setpoint will tell you if the values are getting through correctly.
Another probably simpler method is to just read the MPW shadow values with a program in the T3.
10 T3_VAR1 = 1111AV222
<Where 1111 is the bacnet instance of the MPW
<And 222 is the bacnet object ID of the shadow setpoint
While working on this I noticed that VARS dont have the priority array features, just the outputs have it. I updated the priority array discussion to show the new T3000 UI which shows off the priority array for the outputs.