No, SyncBack cannot run as a service, but SyncBack can be scheduled to run when there is nobody logged on or even when somebody else is logged in.
Running as a service increases the CPU and memory load on the computer as the service is running all the time regardless of who is using the computer. Scheduling does not require the program (service) to be running all the time.
For steps to setup a schedule in SyncBack, refer to this article (see section "Setting a Scheduled Task for your profile to run automatically").