I don't know if it is outright forbidden, but I almost never see it done. Different custom, perhaps from the fact that cemeteries here started in the woods and unattended fires, even candles, have always been discouraged. Indeed, American cemeteries, even to this day are grassy parks where placed flowers are very common and seem to me to be the norm. Just look up pictures of Arlington Cemetery near Washington DC or the American Memorial Cemetery in Normandy, France. Those are typical, albeit huge, American-style cemeteries. The cemetery in Normandy, despite being in Europe, had no placed candles where I was there.
Compare those two to Pere Lachaise in Paris or Powiązki in Warsaw, which have stone or dirt paths.