Good move on checking the finish temp with another therm prior to removal! I had two 8# butts in the SI#2 on Monday, and the Maverick was reading 198IT at just about 8.5 hours. Seemed a bit soon to me so I checked with another therm that read 181IT! I guess my position on the Maverick was not ideal; when I re-inserted into the meat, the temp fell to 183IT. Took another 2 hours to get to 196IT when I removed and foiled the meat for resting.
As to you question...I think you can use the BBQ outlet for another meat probe as they seem to have the same connectors. While I am not totally positive, I think the only point to the food vs BBQ inserts is for the display.