Although I can't prove a direct correlation, I've worked with a musician whose old tube SVT bass head went nuts when we had an artist bring her Theremin onstage at a festival. The unit was fine for the whole festival run, before and after her set, just acted up the one time. I just attributed it to the bass head being within a few feet of the therimin. If it's a problem just move it further, the field shouldn't be too large to be an issue most of the time
