Can only CRM administrators be assigned as approvers?
No, any CRM user can be selected as an approver. These users can be selected from any role, profile, group, or level or the record owner can be selected.
The levels available for selection depend on the number of levels defined in the organization's role hierarchy. You can select how many levels in the hierarchy above the record owner the approval request should be sent to.
In addition to this, all CRM users who have Administrator privileges will be able to view records in My Jobs and approve or reject them by default.