Yes, because the participle needs to agree with the direct object if it appears before the auxiliary verb.
Both "le" and "la" contract with "ai" to make "l'ai" so your only hint to the gender of the direct object is "vu[e]". If it is masculine (vu) then you can infer it is "le" - i.e. him - and if it is feminine (vue) you know it is "la" - i.e. her.