Topic: Intro Guitar chords for "And I Love Her"

Another one for the theorists, to wit, the intro for the  Bb instrument chart I have has the song starting with the ii chord (A-7) and moving to the V chord (G) and then repeating. The guitarist in our band is using a Dm and a Gm chord to cover these chords for the concert key. This progression is seen by me as a the vi and the ii of the concert key F. This seems to be a strange/unorthdox progression. I'd like an explanation of why it works (or doesn't!) and other suggestions. Obviously, what transpires for the intro can then be repeated for the outro (with the relevant adjustments) as the song modulates to the Ab key for Bb instruments (F# concert). As always, feel free to weigh in.