If I move to an enemy battlefield with Twilight Reveler and use Akali Champion ability to bring it back, is the card still considered an attacker?

No — once Twilight Reveler is moved back to base, it is no longer an attacker.

Twilight Reveler gained the Attacker designation when combat opened at the enemy battlefield (Rule 464.2.c.3), but the designation is tied to that combat. When Akali's ability moves it to base, it no longer occupies the battlefield where combat is ongoing, and the designation is removed during the ensuing cleanup — a unit is only "in combat" if it occupies that battlefield and has a combat designation (2026-03-30 rules clarification). Same principle as FAQ #1920: leaving the combat battlefield drops the combat designation.

One nuance: Twilight Reveler's "When I attack" trigger has already fired the moment it gained the designation, and it will still resolve normally even though the unit is now at base — triggered abilities are independent of the source's current state. If it was the only attacking unit, moving it out also unstages the combat at that battlefield.