How could Lord Voldemort have controlled the dementors?

Voldemort wasn't controlling the dementors at all. When the dementors were working for the Ministry of Magic, they were offered very little 'food' ( i.e the happy feelings of the prisoners of Azkaban). read more

Voldemort believes the Dementors are loyal to him, but I'd be willing to bet that Voldemort in turn garnered absolutely no loyalty toward the Dementors. He believed they were under his control: ‘The Lestranges should stand here,’ said Voldemort quietly. read more

Voldemort WOULD become an empty vessel as he has already locked 6 sevenths of his soul in horcrux's so what's left in Voldemort himself IS actually his only soul. If a dementor sucked this out then he would have no soul left in his actual body at the time. read more