If the job simply says "need to hire 5 freelancers", then apply for it. The client is simply looking to hire five different people and you don't need to be in an agency to be one of them.
If the client wants an agency, I think they can request this right in the actual job posting.
Kennedy, be careful with jobs that say they need to hire 'x' freelancers. From what I've read in this forum, several freelancers have applied to such jobs and discovered that the job was a scam.
"No good deed goes unpunished." -- Clare Boothe Luce