You could really look at it either way. If you treated that progression as a descending ii V progression, as a practical matter, you would be using the same finger patterns for the Em7 to A7 and the Dm7 to G7. I prefer looking at it diatonically because from a theory standpoint I know that all of my lines are based from one scale (C Major) with the addition of a few passing tones here or there to add color to the line. (Gee Chris, where did I get that idea from???)