Based on info from the games:
-The final attack Julius used is unknown
-Dracula's power was separated from his castle, as the castle was eclipse-sealed by the Hakubas
-A Belnades and Alucard had assisted in the fight
-SPECULATION: Based on the fact that Dracula got a "second chance" as Soma, he may have found redemption at the end, and true redemption (more than what he experienced in SOTN) would indeed break Satan/Chaos's power over him.
Yeah, there's a decent chance he used Greatest Five. Maybe, but maybe not.