No. In some cases, an owner will lease the property directly. Sometimes, the owner will employ an in-house leasing agent. Typically, these are called open listings, where the owner will pay a full commission to any tenant representation broker who brings a tenant to the property. An in-house leasing agent is usually paid on a salary basis, so their incentive to enter into a lease is different that from a listing agent who is paid a commission.
It is also essential to understand that when you are negotiating with an owner, the terms of your lease take on a much greater importance. The owner is going to receive your entire rent payment, while the listing agent receives only a small percentage as his commission.
Also understand that if you hire a tenant rep, there may be a conflict of interest when viewing an open listing. He may get paid a full commission on the open listing, since there is no listing agent to split the commission with, versus receiving a half commission on a listed property. So be aware whether the listing is open or not.