The 1/4-32 spark plug ignitions have the resistor in the cap also. I've flown the Rcexl ignition with no resistor without any problem but not on 72 mhz analog radio systems. Do a thorough range test with the antenna pointing in all directions and engine running at all RPMs and see if you get any problems.

The vendor where you purchased the ignition should have no problem exchanging it for you if that was your desire.