Yes, I use FTP to transfer pictures to my iPad. I'm using the plugin http://regex.info/blog/lightroom-goodies/collection-publisher
to create the published folders on my hard drive that the FTP client built into the plugin will synchronize with the app PhotoMgr Pro on the iPad. You need to start the FTP server on the iPad and be on the same network to do it. You should be able to use this with any FTP server, but I have only used it with the iPad app as mentioned. The reason I use this way to synch with the iPad is that I like that PhotoMgr Pro can sort images the way I like on the iPad and that you can have nested folders which you can't with the built-in iTunes synch and the standard picture viewer on the iPad.
Edit: Adding that the FTP client built into this plugin will also be able to synchronize the content with the remote FTP server including deletes and modified files. The publish part is done separate from the FTP synch part.