A stereo pickup is not used on an electric guitar nor on steel drums since they are mono but maybe steel drums can be stereo.
A stereo pickup was used on vinyl records (remember them?).
I have never seen an amplified steel drum. Ordinary drums use piezo transducers to pickup their vibrations.
An electret mic would be overloaded by a very loud close-by steel drum.
An electret mic and its preamp can pickup any kind of sound. Since a steel drum is loud then the gain of the preamp should be fairly low.
If amplified speakers are close to the mic and the mic can hear them then of course feedback howling will occur.
The 470k pot in my preamp circuit sets the gain. Reduce its value to reduce the gain.
If the gain is turned down but distortion is heard then the mic is overloaded by sounds that are too loud for it.
The metal housing of a mic has vents at the rear of the diaphragm to produce a cardioid pattern. I have an Audio Technica electret gooseneck mic made like that.