As has been stated DME does indeed transmit.
To proprly test for EMI you'll need a licenced radio engineer. The DME PRF (pulse repetition frequency) is different when a DME is searching for a ground station and when its locked on. The frequency will vary according to the co-located VOR frequency selected but its in the L-band region which is a little above 1000Mhz.
Transponder is similar and there are different pulse characteristics for the different modes. A test using the approprate ground test equipment should be carried out. (unless of course you'll do these tests while flying, which I doubt)
IMHO unless you do these checks simulating an operating situation the EMI checks would not be valid.