Depends on what you consider Zoro's character to be imo, unlike Luffy and Sanji his hasn't been firmly established yet, though this King of Hell idea could just be the start. Zoro's had demonic moments before, absorbing an enemy's haki and turning them into a husk before using it to throw off a huge attack easily isn't something that would destroy Zoro's character. Then again I'm more focused on improving Zoro's versatility and entertainment in fights than the power itself.
One of Zoro's opponents has already had this ability, Enma.
Lmao his haki is already at the highest level, if he can cut Kaido and King already, improving that stat won't change anything in his future fights.