I haven't received an answer to this question or found any documentation, but looking at the DNS settings I see that for a hosted domain DreamHost creates a number of A NAME Records that point to an IP address.
Some of these are for subdomains I've created, but I believe two are determined only by DreamHost and cannot be edited. These, I believe, correspond to the naked domain (hpmtb.org) and the www prefix.
If I try to create a new subdomain called 'www' I'll get an already hosted error -- because there's already an A NAME record I cannot edit.
I'm guessing that if one configures a domain as fully hosted with Dreamhost it's NOT POSSIBLE TO REDIRECT WWW OR DOMAIN THROUGH THE CONTROL PANEL.
It is likely possible to do this using htaccess:
I experimented with redirects on a non-fully hosted domain and it appears I cannot create 'www' as subdomain, attempting to do this with a redirect may simply redirect the entire domain.
I plead for help on app.net and my request was immediately answered.
For practical purposes www and domain are one and the same. One cannot redirect www separately from domain, fully hosted or not. I think I need to use Apache redirects by editing htaccess.
(Some providers support DNS level URL pagerules but Dreamhost does not. CloudFlare does, an option for Dreamhost customers I believe.)