Within a project you can invite contractors to contribute hours.
Contractors are not like staff members in that they only have access to a particular project and all of their financial information is segregated from your Account. When you invite a contractor, they're asked to create their own Ronin account. From within their own Ronin account, they'll be linked to your account via the shared project.
Your project rate and hours are not shown to Contractors. Similarly, your tasks are not shown to them unless you assign a specific task to the contractor. From the contractors view, they're allowed to set their own project rate and create their own tasks. Their staff users can contribute hours and they'll simply show up on your project as originating from the contractor.