No that is not correct. Also, its already clear: "Mail comes in and gets scanned by the anti-spam machine. If it's okay, it gets passed on to your normal mail servers and goes in your INBOX." That has nothing to do with webmail.
However if mail is quarantined it can either be delivered to a subfolder or kept in a database. If it is kept in a database, you have to use a separate function to read the quarantined messages and/or take action on them. DreamHost maintains its own Squirrelmail webmail client and has modified it to provide a link to the messages in the database. You get to chose whether or not you want quarantined messages in the database or subfolder.
Also since the junk mail filter is maintained by DreamHost, they provide a web interface to the settings you are allowed to change.
You're free to host the web site at DreamHost and have your e-mail hosted elsewhere, such as with Google, since you can change the MX records. Other than it appears what you want is a dedicated e-mail server which is not something that is offered.
This is no longer an ideal solution due to restrictions in place to help prevent spam. The problem is that there are quotas on how many messages can be processed and the procmail solution effectively doubles the number (forward to shell, then forward to mailbox). Not to mention putting additional load on servers meant for running web sites might cause you to be flagged for resource abuse (unless you get this to run on DreamHostPS instead of shared hosting).
Customer since 2000 openvein.org | Please don't feed the trolls. :@