Powers & Abilities Are Hakimans the only ones who can use Emma?

[Rootbeer]

because he cant be damaged with flames.

Wrong assumption.. Zoro has never used KoH with flames..

King of Hell with green fumes is a Zoro-only thing

Not necessarly just as CoC coating was not displayed before Luffy unlocked it, the same can be said for Enma mode not being revealed before Zoro stabilize first.. Power up reveal..

 

[Momonosuke]

The whole thing with enma acting up could have been because of kaido so enma could be calm now

 

[Santoryu D Bazooka]

You didn't get it. Read the title "(E"M"MA)