I used a GL2 with UV and Tiffen Soft/FX 3 filters to record an opera performance. Not having seen the production before, I had no clue as to what the lighting was.

Everything was fine except when the red lights came on as key, backlight or background. Everybody had a pronounced red glow emanating from their entire body, much like an energy field. Under every other lighting color - shades of blue, shades of green and white, there was no such hazy glow.

Could I have done anything to minimize this?

Sounds like some sort of flare issue. Depending on the offending lights location you might have been able to alleviate it with a change in camera location or a larger lense hood. Both of which, I know, are impractical...knowing you set up on your tripod/etc prior to the show start.

I'm sure the Tiffen Soft/FX filter perpetuated this visual abnormality as well.

I figured the filter was a contributing factor, but am puzzled as to why it is sensitive to red only.

I was out in the house, some 75 feet from the stage. The lights were all located over the stage, or perhaps in the ceiling and catwalk over the orchestra pit, slightly in front of the stage.

I've done around 7 dance recitals with my GL-1 and have noticed that it is really sensitive to red light. What's worse is that most dance companies want to use red a lot. I once had a dance group that had shiny red outfits with nothing but red light. OUCH! The only thing that I have found is in post, I can turn down the saturation a little seems to take out the red glow. It may or maynot make a noticeable difference in the rest of the video. You could experiment with the settings in the camera that control color a little. Good luck.

Have a look at the chroma level on a vectorscope (hopefully your NLE was one) The reds are most likely way over saturated.

Most theatre lighting is a real pain for video as there is never enough base light, their white light is never white enough or bright enough (some fixtures are only 2900 degrees K).

I don't know what the cause is but yea, I would suggest pulling the chroma down at least to video legal range and see what that does.