If the boys play this in G can I play an F dorian over the progression? If they play it in A can I play a G dorian? Want to shape the tune a little. Just don't know if it would work. Sorry if this post is out of line for the topic.
You have the right idea but not the right scales.
If the dead play it in G, you can play the following scales:
G major (Ionian)
G pentatonic (maj or min)
You can figure it out from there for any other song you want. If you have any questions about how I arrived at these scales just ask.