Probably unless he does exceptions.
You know what isn't concrete? How the Headliner system actually works.
Now explain Hawkins being a new member and the implications he'd have to challenge a Tobi Roppo.
Doesn't change the fact Oda doesn't always state one's position within an organization.
Show me Bege being called a Fighter like Pekoms and Tamago.
Not saying Apoo is a Headliner, but there's nothing conclusive to rule him out. Even if he weren't a Headliner, it'd do nothing to answer how the Headliners rank works.