Yeh baro Is used as well as DME but If the ILS Is out then It would have to be a visual approach I guess or use an alternate Airport .
A lot of Airports are starting to use approaches aproved for GPS as the latest GPS are TSO rated for this . I.E they will provide vertical guidance due to the Increased accuracy of the GSP system They also run Baro Info to the GPS for redundancy If a satellite become unusable.
Can't answer the 737 issue I only deal with Helicopters S76,sorry.
May be part of the Ground Prox system ? as the Rad Alt would be part of this?