I've been composing a song, using the chord progression Am - G#° - Dm7/A - E (i - VII - iv - V), that is using the Harmonic minor scale. 

The song has some melodies, that happens in different parts. The melodies are following the harmonic minor scale, but sometimes, I use the G note, instead G#. 

The melodies that uses the G note sounds good to me, but I don't really know if this relationship between the two scales are a right pratice. 

Can I mix natural minor scale and harmonic minor scale at the same song? 

Can I play the G note, when the G#° chord is played?

Thanks a lot for the help!