Can Dante Use Yamato?

Both Dante and Nero wield Yamato in Devil May Cry 4. Nero's use of Yamato is limited to when he is in Devil Trigger, and even then he only has a few attacks with it. While in Devil Trigger, Yamato also grants Nero the ability to use a slightly different version of Summoned Swords.

Is Nero's arm the Yamato?

Nero's arm was taken by a mysterious figure in the first stages of the DMC 5 story, we learn that person was Vergil who was sickly but looking to gain absolute power from the underworld. He used Nero's arm, the Devil Breaker that absorbed the power of the Yamato, to regain the sword.

How does Dante transform?

In Devil May Cry 3, Dante gains the ability to Devil Trigger after his first fight with Vergil. After losing to his brother, Dante is impaled with Rebellion. His blood awakens his demon power and he is able to transform, and becomes much more powerful.