To find out if the partitions are hash or range :

Select * From SYS.DBA_PART_TABLES

(look at the PARITION_TYPE column)

If 3 of the 4 tablespaces are empty, why don't you drop them from the database? The command is 'Drop Tablespace <tablespace_name>'. (then go and delete the corresponding datafiles at the OS level, because Oracle does not do this for you.)

Then when you need the space you can create the tablespace again.

This way you don't have to worry about if it is safe or not to exclude them from the backups. (By the way. you can just exclude them from backups, but it makes recovery a little trickier.)

-John