if a quad has motors that are not equdistant as in the pciture below. Is it neccesary to make adjustments in Ardicopter to compensate for the difference?
Note, the picture is just for refece to explain the point and not the actual dimensions
No, it is not necessary. But it might slightly improve performance if you do it. Take a look at the lua mixing script example for inspiration if you really want the extra 0.5% performance and are willing to work for a couple of hours on it.
No. I have built all manor of frame geometries using Quad-X for all of them w/o issue. Even if they look like H’s or V’s. Some may have more or less Pitch/Roll/Yaw authority because of it but not a big deal.