The flight numbers will unambiguously tell you if the operator is United or a UX partner that United treats as UX metal.
Look at page 10 of
http://www.uatimetable.com/United.pd...+timetable+PDF
As of May 1, 2009, a flight number between 1 and 1099, inclusive, is United (looks like the Ted-era numbers are gone ^), and a flight number between 5650 and 8099 is United Express (UX). Flights in those ranges will earn DEQM.