Any titling that you make in FCP will be permanently embedded in the finished video.
Do it in DVD SP with a text file made in TextEdit. Give your viewers the option of turning it off.
Stolen from the DVD SP User Manual...
Preparing subtitles for use in DVD Studio Pro:
> Note: If you specify a font to use, no subtitle
clips will appear if the font is not found on the computer that will be encoding the DVD. The font must be installed as a Mac OS X font— Mac OS 9 fonts are not used.
$FontName = Arial
$FontSize = 24
//If you need to include comments, place them on their own line, preceded by a forward slash, a space, then another forward slash like the example here. This text will not be superimposed over the video.
00:00:12:04 , 00:00:14:12 , This is a subtitle...
00:00:16:14 , 00:00:19:08 , ...followed by another subtitle.
//Comments can also be placed between subtitles.
00:00:22:08 , 00:00:26:15 , This is the next subtitle.
and I'm pretty sure that TitleExchange pro will allow you to take the work you've done in fcp and bring it in to DVDSP for use as a subtitle track. It's a little tricky but doable (although it's been a few years since I've had to deal with it). The author of TitleExchange pro was very helpful when I had some problems.
The usual workflow is to export a quicktime with a timecode window (that reflects the sequence timecode) and have a translator create a doc with translation and timecode formatted as Nick described in his post. This file can then be converted in TitleExchange pro to be usable in both dvdsp and fcp. There are other apps available with the same functionality.