If unmatched impedence signal radiate EMI, will it be also more susceptible to EMI?
The reason an impedance mismatch radiates EM waves is because not all of the energy is delivered to the source/load. That energy is converted into EM radiation, and the transmission line works as an antenna.

Antennas have the important property of reciprocity. This means that if you reverse the transmitter and receiver antennas, you get the same result. So yes, if the same EM field is present at the transmission line, it will generate the same current/voltage. To clarify: this is the current/voltage not absorbed by the source/load.