Yes, it is not essential to own the cars you rent out on Getaround.
You need to have a written authorization for the person (physical or moral) who owns the car (such as a lease agreement), as well as a copy of the registration certificate under his name. You’ll have to provide a copy of this authorization and of the registration certificate to the driver (for example, you can hire the car of a relative or a leasing car, as long as you have a written authorization of the owner to do so).
This article contains information specific to certain registration countries. Please refer to the international version of this article for other cases.