All OSM tags are loaded from the OSM data primitives are loaded as FME feature attributes. Relation feature types will have their members mapped as an FME list attribute in the FME feature. The list attribute will have 3 components:
member{}.type
member{}.ref
member{}.role
Relation feature types will also have an attribute named as osm_relation_type to describe the type of relation.
You can use this member list attribute to further process the relations within FME Workbench.
In OSM way features are constructed by reference to node IDs. These node IDs are mapped into the nd{}.ref list attribute in FME way features.