I had much better success with dbms files with datatrieve. dbms is more of a "networking" database, and using datatrieve helped propogate key candidates to be used as foreign keys in the destination. The vms dump utility might not be as well suited here. We routinely dumped dbms data into oracle, but we used datatrieve so that we could make sure that member records had the key of the owner record because while dbms links its records using a sort of linked list, when using this linked list, you had an implicit relationship which must be made explicit in the destination relational database, that's why we would propogate the key from the set "owner" to each extracted set "members" (if I remember the terminology correctly LOL)
edit: the unload routine will indeed move data so you can use the key in the "owner" record in the "member" records for each set so you can use that in your relational database.
another concern to keep in mind is that numerical data might remain in DEC's data type format in the rms files, we used datatrieve to get around that by simply formatting numbers into text.