Defined benefit plans - borrowing

ERISA does not bar plans from obtaining a line of credit/loan from a bank or other financial institution, but assuming the bank is a party in interest, is there consensus about the ability to rely on 408(b)(17) service provider exemption (adequate consideration requiring reasonable interest rate/terms).  And if collateral is required, do parties take the position that posted collateral is not plan assets, similar to collateral posted for derivatives?