No it isn't. The protection mechanism used a few years back was nothing more than a small resistor running from the sleeve to ground, which was why shorting the sleeve to the BNC connector would restore full external audio levels. Running a discriminator signal through that return path would have no effect on decoding whatsoever.
It's only with circuits like this...
http://home.ica.net/~phoenix/wap/BC246T/Audio.gif
...where you have to spend a bit more time:
- remove 18 ohm resistor and connect sleeve to ground
- remove 10 ohm resistor and connect ring to discriminator
- wire discriminator plug to use ring and sleeve
- if external speaker/headphone functionality is desired, wire its plug to use tip and sleeve and install a DC blocking capacitor (100-200 uF) in series with external speaker/headphone
- if jack will not be used for external speaker or headphones, VO2 can be connected directly to internal speaker