Not quite sure how this would have any effect on the kill switch. The kill switch just grounds the low tension side of the coil.
The RF generated by the pulse going up the tacho pic up wire running alongside the kill wire will do nothing. In fact the coil side of the kill switch already has a pulse on it, which I have verified with a scope and I use this pulse to calculate the rpm on my Paramotor Engine Monitor I'm working on.
Is the Tiny Tach powered from the motor rather than an internal battery? If so there could be an issue there.