Is the Hadith that states: "Whoever passes by graveyards and recites 'Qul Huwa Allahu Ahad' (Say: He is Allah, the One) eleven times, then dedicates its reward to the deceased, will be given reward equal to the number of the deceased" authentic?

This hadith has no basis; it is among the fabricated and false hadiths. It is not part of the Sunnah to recite the Quran at graves or among them. Rather, the Sunnah, when a Muslim visits graves, is to greet their inhabitants and supplicate for their forgiveness and mercy.