Can I Use a Filler to Fix my Scar from a Belly Piercing?

A careful examination is necessary to provide an accurate answer.  However, there currently is no such thing as a "permanent collagen filler."  The closest thing to a permanent filler is Artefill, and I do not believe that I would recommend injecting it into this area.  After careful examination and discussion with your surgeon, you might consider using an hyluronic acid filler agent such as Restylane or Juvederm.  A small scar revision may be your best choice, but I am not able to tell from the photograph.  Good luck.

There are a couple of options to consider in an attempt to improve your scar.  I really don't thing a filler alone will improve things.  You could consider have the depressed scar surgically removed and the incision re closed.  You would still have a scar but hopefully a finer scar that is not depressed. 

A second option is to do a subcision (release of the scar tissue from the underlying fat/subcutaneous tissue) and then inject a little fat into the area that has been released to plump up the depression.

There is no collagen filler that is permanent. Some last longer than others but none of them are permanent. Fillers don't fill this scar well. if it bothers you you should consider a surgical revision. This might create a scar but  the depression/hole can be improved.