Can I add a Manager or Coach in 'Reports to' in Career Overview/Job Information that is not an employee in this payroll? So I can assign employees to this person.
Yes, you can. In that case you can create this Manager as an employee with the status 'inactive'.
In that case this employee will not be added to the periodic payroll, but you can select this Manager in 'Reports to'.
And if you keep the same login name (e-mail address) as the login name of the existing account of this Manager, then this person can log in only once in his/her account and switch between the different payrolls and related rights.