You can use export and import to migrate tablespaces to OATM, in cases where OATM is unable to do the migration without errors:
Here's how I tested:
Export a table
Drop the table
Change default tablespace of user to a new tablespace (Done by OATM automatically)
Drop the tablespace in which the table existed
import the table.
Table now exists in new tablespace.
This is not supported by Oracle and you should do this only as a last resort.