Eric,
I know it is frustrating but give the dealer a little more time, thought sticking to make sure the issue is fixed. I would not see it as fraud, unless they intentionaly sold you a known bad bike. Does not seem to be the case, more along the lines of a problem that has not been nailed down yet.
On the binding of the grip, by chance did they take apart the controls for some reason. The reason I ask is that many times when reassembling the right hand controls, the throttle grip get pushed up against the bar and will bind, it normaly is just a slight adjustment on the placement of the grip to take care of the issue. Yours may be something else, but hopefully a simple bit of lossing the grip and control and sliding very slightly to the outside to insure that grip is not binding.
Is the OP gage that you are using, installed in the same place the dealer installs? Also when the light comes on, is it only at idle or what RPM. Make sure that the idle is not set too low also. These engines need to have 1000 RPM for idle and not the somewhat typical low potato potato idle that so many HD like to set. If the idle is too low could be causing the OP sensor to light up due to low of RPM and thus lower pressure.
Have they checked the oil pressure sensor by the way. A good way is to take it off and put an accurate pressure to it like from a gage calibartion set and to see where it changes status from Normal Open to Normal Closed and vice versa. Barring that if in doubt, just put a new one on to make sure it is okay.
Good luck and if possible work with the dealer, but stick to your guns and have all issues address. Hopefully it is all something simple and can be taking care of quickly.