Center/Hub Managers are considered Business Managers in training materials and policies. The difference is job classification. The level in the hierarchy is no different than a PT or FT Supervisor, e.g: Hub Supervisor or On Road Supervisor. Many UPS positions aren't in GEMS as official titles.
CEO/Board/Cabinet
US Operations President (assuming you work in the US)
Region Manager (or you may see them referenced as President)
District Manager (aka President)
Operations/Transportation Manager
Package/Hub/Feeder Division Managers
Center/Hub/Hub Training/Feeder/Engineering/Labor/H&S Managers (some of these may actually oversee large portions of the division/district and multiple buildings)
FT Supervisors
PT Supervisors/Specialists
Hourlies
As to not confuse things, Supervisors comprise may job classifications and some can be PT, some are FT (for example, CHSP positions are FT only), some are both: Hub, On Road, Feeder On Road, IE, PE, Center, Dispatch, Package IE, District CHSP (don't let the word district fool you, they are really tied to a division), H&S, Hub Training... I'm sure there are a few more.