TextMate works wonderfully well with Yummy FTP as a remote editor too. Just select it as your default editor from the menu in the Server Options panel of the Preferences.
Another possible solution is an 'Upload Only' FTP Watcher. This will monitor a folder for changes and upload changed/new files, however it does only work at the folder level at which it is placed, so it will not detect changes within sub-folders. FTP Watchers will not upload changes immediately, but they do check for changes about once a minute. A description of the use and configuration of an FTP Watcher can be found in the Quick Start - select 'Quick Start' from the Help menu in Yummy FTP to see this.
Finally, a synchronization scheduled to run perhaps once every minute, would do the job of an FTP Watcher but would cover the entire hierarchy of the folder on your Mac.This won't instantaneously upload changed/new files, however. Again, a description of how to configure this is available in the Quick Start.