You can in theory use any 2 microphones for "stereo", but It is also nice to have a pair of the same mics so that the signal will be balanced. I use pairs when recording the band or orchestra at the local high school. That way I don't have to guess at the EQ for each channel. I just use the same levels and flat EQ on both. The stereo image is awesome with the mics out front about 20 feet apart!
Sincerely;
Dom Franco