Bass note refers to the note having teh least pitch. eg. a chord being played is E minor then the notes being played will be: E, B, G now u could play the chord in a way that E becomes the bass note, or u can play making B or G as the bass note - this is known as chord voicing.
SO Em/G IS Em with a G as bass note can we use any other notes other than B andG as alternate bass for Em
You can use pretty much any note you want to.....only if you want the chord to be Em, play it with an E,G or B bass note.
I think what he meant was that if you use any other note will it still be Em It will..but the tonality will be slightly different. For example if you use a C, the chord will be called Em/C. An example of this would be With or without You, where ones of the guitars is playing only a D chord with changing bass notes.
