its unlikely that the arm itself has seized solid.
do you have software and cable for your car? you can use FiatECUScan to run an actuator test on the VGT system which should help you. I doubt you are going to get a vast amount of movement with the engine at idle anyway.
it is always a good idea to keep that arm greased though, I tend to pop a bit of grease on the arm whenever I am poking around under the bonnet, just to be sure.
Although I've not tried myself my mecnanic did tell me you can suck on the pipe to try and get it to move, not sure if thats going to work or not though lol
typically when people get overboost issues, which I am assuming you have, then vacuum pipe tends to be suspect number 1, its easily replaced for about £2 so may as well rule it out. there are two bits of pipe to replace.
one that runs out the bottom of the turbo VGT mech up the back of the rad and into the VGT solenoid on the top of the radiator, then another bit that goes from that solenoid across the top of the engine to the hard pipe which comes from the vacuum generator.
you can replace the pipe and see if that improves your situation.
if you have any information from diag software that would help too, like when is it overboosting, is it overboosting constantly or just certain revs / certain gears etc.