Can a doctor go through the belly button to preform a gastric sleeve surgery, to avoid scaring?

Yes: Yes some advanced surgeons can do this but not that many. Generally even the surgeons that are capable only do the single incision procedure on specific patients. I do this procedure in my practice but the incision is not through the belly button. But a few centimeters higher instead.

Bariatric surgery: See a qualified bariatric surgeon to discuss your options and get a second opinion if needed. There is a possibility of going thru the bellybutton laparoscopically or with the robotic approach but the sleeve may not be your best option. Overall diet and excersize is always best and you would not have any scars at all.