Is there a lotion I can put on my arm to increase healing and reduce scarring from a fistula placement?

Yes. Occasionally silicon jell ointment will cause raised scars to flatten. Nothing will erase surgical scaring.
Sure. After the initial healing period, many people use aloe or vitamin E on the scar. Arnica can help with postoperative bruising and swelling. Other over-the-counter scar treatments like scar guard or silicone sheets can reduce the appearance of dark or hypertrophic scars. Ask your surgeon before using anything on the scar.
Mederma. This can help but need to speak with ur surgeon to make sure the incision is ready for this.
Not really. Ask. Ask the dialysis nurses or your nephrologist for advice about skin changes after fistula placement. They have plenty of experience with these issues and will have several options that will not be harmful. Scar gels and ultraviolet avoidance can reduce the visibility and firmness of scars somewhat, but unfortunately scars are permanent. Fortunately, they fade and soften. Good luck!