Yes, Vibhīṣaṇa also killed some rākṣasas during the battle between Lakṣmaṇa and Indrajit. Bow & arrow seems to have been his chief weapon.
Seeing Lakshmana and Indrajit, fighting with commitment to gain
victory one over the other, like elephants in rut, that strong and
valiant Vibhishana, wielding his excellent bow, stood there at the
battle-front, with an intent to behold their combat.
Standing there thus, Vibhishana stretched his great bow and released
excellent sharp pointed arrows on those demons. Falling in exact spot,
those arrows, hitting like fire, tore the demons into pieces, as
thunderbolts would cleave large mountains. Even the foremost of
demons, the attendants of Vibhishana too, rent asunder those valiant
demons in battle, with pikes, swords and sharp-edged spears.
Surrounded by those demons, Vibhishana shone like an elephant in the
midst of proud young tuskers. Vibhishana, who knew the timing, spoke
to the monkeys, who cherished to destroy the demons, the following
opportune words duly inspiring them. "O chiefs of monkeys! Here stands
before you, one [Indrajit] who is the last support of Ravana. He is all that is
left in his force. Why do you stand idle? At the end of this war, if
this sinful demon is killed, the remaining army is as good as killed,
(Valmiki Ramayana - Yuddha Kanda in Prose - Sarga 89)