If I purchase VIP GA and my friend gets general admission, would I still be able to stand in general admission with them?

In theory, yes. However VIP general admission tickets often include early entry to the General Admission section so they will be in this area before general tickets holders and it may be difficult to find one another based on demand and arrival times.

Some tours also have VIP specific standing GA areas that may mean you are separated. Be sure to review this based on your particular event.