Position Hierarchy questions

I have a client whom has one Purchase Order Hierarchy. It contains more than one Operating Unit (OU) used for Approval Groups/Assignments. For example, Taiwan OU and Cayman OU.

There is one position which they want to approve all purchase orders (i.e. Cayman Manager). Some positions under this Cayman Manager position have a higher approval authority than the Cayman Manager has.

My questions are:

1) Can you combine approvals amongst separate OUs which have different currencies? In other words, can a Taiwan OU Position's PO approval flow up to the Cayman Manager (Cayman OU)? Or does the Position Hierarchy have to be set up and functional within just one Operating Unit (set Cayman Manager up with Taiwan approval group assigned to approve any Taiwan POs)?