"For stereo, use directional cardioid mics, close together, aimed opposing at 90 degrees."
That is just one stereo technique, and it is neither the best nor used the most (actually hardly at all) by audio engineers who specialize in recording sound for a living.
Don, ORTF and spaced omnis are standard methods of recording stereo with two mics. What is hanging from the ceiling for concert recordings could be either an ORTF configuration, spaced omnis or even a "Decca Tree," which has three mics, the middle to fill the hole from spaced omnis. There is also Blumlein, mid-side. . Some companies use scores of mics for different sections as you say, but I am just talking about two-microphone stereo techniques. And placement matters a lot too. Most professionals I know prefer two-mic techniques for recording natural acoustic music, but often recording live concerts dictates closed-space multiple mics because of an obsession with quiet.
Two mics at 90 degrees with some kind of spacing (if no spacing it's likely XY, but that is rare) is not a well-respected stereo technique and I do not know any professional engineer who does that. I did not say anything about "separation" for the sound field, just the mic spacing to achieve good sound, as measured by multiple dimensions directionality, frequency response, depth, width.
Now, whether these classic stereo, two mic techniques will work with combinations of camcorders' mics, I agree we can't know without knowing their specs. But I know what I need to find out. Anyway, this is just fun to think about. One could just more easily just set up two mics and plug them in, as you say, but certainly not with an arbitrary spacing at 90 degrees! And cardiod has limited bottom frequency response compared to omnis, and often more noise at a similar price point.