If one uses Single Point Ground (SPG) practice by having two leads coming out of the battery, I do not see a problem as I do it myself in 3 different setups. It takes surprisingly minimal inductor capacitor (LC) filtering if at all to quench any voltage ripples (conducted emission or CE referred to in EMI/EMC testing). Besides, the capacitor discharge ignition that we use empties the stored energy after every spark since it uses a self-commutating SCR (silicon controlled rectifier) to fire the plug. The harmonics that cause electrical noise is very minimal.

I have looked at noise caused by high voltage discharge ignition and noise caused by metal to metal scratching on my scope. Metal to metal scratching is one order of magnitude worse. It will make servos jump or cause a fail safe in the receiver. Whereas, having continuous spark from an open face plug placed next to the receiver did hardly anything to the received rf.