I wouldn't really worry with drafting holders. Like GTWMA said, there really isn't a way to predict the top holders outside of the usual suspect setup men (a handful at best). There will be plenty of holds on the ww throughout the year since it's probably the most volatile position for numerous reasons. That being said you should be able to find enough during the year to at least be competitive if not lead the league if you do your homework.
In a league where you have lots of guys who understand holds, however, the best holders (like Gordon, King, etc.) will disappear between pick 250 and 300, usually. You can identify the top 15-25 holders, almost all of whom will rack up 15+ holds, unless they get injured or moved into a closer role. So, while you can be competitive in holds without drafting one or two of the top guys, you can't win it, unless you destroy yourself in WHIP and ERA.
Holders are also great throw-ins to even up trades in these leagues. Otsuka helped me get Derrek Lee at the end of last year from a contender who was trying to grab a few extra points in holds.