Fillers or Buttock Implants for Tailbone Sticking Out?

if this is the tip of the coccxys, it can be removed or shaved. Coccxygectomy is done for pain, very mobile coccxyx can be painfull. The scar is placed on top of the coccxyx and heals very well. Post operatively there is pain when sitting mostly, for three weeks
Butt implants will not cover it.
Fat graft as a filler may soften it but it is the wrong area in the buttock to fill with fat.

Implants will not help to cover the prominent bone over your sacrum. If the growth is coming from your coccyx, I would resect it. If its excess growth from your sacrum this can be burred down.
Fat transfer or fillers can be used to fill this area but it can make this area of your lower back look fat and unattractive, blunting the pre-sacral recess, causing you to lose the heart shape to your buttocks.

 Buttock implants will not be of any value to you. Fat grafting of some of your own fat will be able to contour this area with a reasonable result. I don't think that there are any other fillers which could be of any help to you.