Is it ever useful to add a capacitor between op amp inputs?
I think he got lucky- that hairball haywired circuit probably had some inductance that caused the oscillation. High currents only require a small layout issue to cause feedback voltage to show up- at the 750kHz that he reported and several amperes it wouldn't take much. 

In answer to your question, yes there is a valid reason to use such a capacitor even though it generally reduces stability. It has to do with EMI sensitivity of op-amp front ends which can produce an apparent DC offset via nonlinearity of the front end response. Since low level signal generally require high gain, stability is less of an issue than it would be with a very low gain circuit.