Cluster tips exist because file writing operations do not write past the end of the file, that is they leave in the bit of the final block they do not use any data that was there previously. FTP is simply writing the file data to the remote server; as far as I know, only the file data is transmitted. Of course, once the file is on the remote server, there will be a cluster tip there, but it will not be the same one as was on the local drive, and there is nothing the user can do about it. If you value your privacy, never FTP unencrypted private data to a remote server!
To add to Joel's point about optical media, CD-Rs and DVD-Rs are write once media, so any cluster tips (I too don't know whether there are any) will be empty. But once data is written to such media, it is never overwritten. With RW media, you would have to overwrite the whole disk to ensure than anything that was previously stored on it is erased, and even then I don't know whether techniques are available to recover overwritten data from optical media. In practice, I think that the only way to 'erase' optical disks is to destroy them physically.