My thoughts are this rumor is completely false. The fly, known scientifically as Sarcophaga aldrichi (Diptera: Sarcophagidae) and commonly as the "friendly fly, is a native insect. It occurs throughout eastern North America and has been helping to control forest tent caterpillars for thousands of years.
Also, the state agency that is charged with protecting our forests from invasive insects is the Michigan Department of Agriculture and Rural Development (MDARD). If a new biological control agent were to be released in Michigan, it would be done by MDARD not the DNR.