backing up an indexes-only tablespace?

Here's a question I can't seem to find an answer for in the manuals.

If I create a separate tablespace on a different physical drive just for indexes, and I'm doing backups of the physical files (from a shutdown database at night), do I need to backup the files for the indexes tablespace?

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Michael Nolan, Tailored Software Services, Inc.
Lincoln, Nebraska
Sysop for the GEnie DBMS RoundTable
nolan_at_notes.tssi.com, dbms_at_genie.geis.com