In the DreamHost Web Panel, go to Manage Domains and for your domain, under "Web Hosting" column click on "Edit"
Now look for the setting that appears as below:
Specify your web directory: /home/username/[your domain here]/
This means DreamHost expects you to upload the file to /home/username/yourdomain/index.html and apparently RapidWeaver isn't doing that.
I don't have RapidWeaver, but looked through the manual for version 4 - eh, they don't go into details.
The manual shows a box with "FTP" highlighted and one of the settings it ask for is "Path"
Have you tried making sure path reads /yourdomain ? I don't think it needs a trailing slash, but it might... Oh yeah in the event you are using SFTP you might need to change "Path" reads /home/username/yourdomain instead - there is a difference between FTP and SFTP.