Using gnd pin as a -vcc pin in LM358
Yes. They specify "Gnd" because this op amp is marketed as a single rail device, but what is ground is arbitrary. If you have -12, 0 and 12V rails, relative to ground at OV, you can connect your ground to -12 and consider them to be 0, +12 and +24 and the op amp has no knowledge otherwise.

It's just the negative supply rail. In fact I've got a circuit right here on my desk that uses LM358s to control 12V fans, which are connected so that the fan negative is at -12V and the fan positive (via control circuit) at 0V, and I used 358s precisely because they can pull all the way down to that negative rail.