You can run Revo just fine without FastCGI (I run it without FCGI and haven’t had an issue yet). The devs will correct me if I’m wrong, but I believe the main reason behind the FastCGI requirement is to prevent permissions/ownership issues.
For example, suppose you do a "Traditional" install first, in which you upload all MODx files. These files will be owned by the FTP user. Then suppose you want to switch to an "Advanced" install so you can change the locations of your core and manager directories. Without FastCGI, you will likely run into some issues here because the installer will try to unpack the manager and connectors files -- but since the existing files belong to the FTP user (from the previous upload), and the installer is running as the Apache user (usually "apache" or "nobody"), it cannot overwrite the old files with the new ones since the ownership doesn’t match.
Similarly, if you want to be able to edit files in the MODx file manager, the files must be readable by the Apache user. But issues arise when you want to update them via FTP - again, the ownership doesn’t match, and the FTP upload process will fail. I’ve gotten around this by giving ownership of the files/folders to the account user and the "apache" group, which seems to work well for me at the moment.
But since you’re running SuPHP, you won’t run into the problems anyways, since Apache will run as your account user and all files and folders will belong to your account. You should be fine to run Revo.
