Still at work, but wanted to pop in to say this isn't true. Users have tested and Nordland has confirmed over at the ulmf forum that the slayer cards do indeed do exactly as described even for this PeroColo event. Just gonna leave the link as I'm short on time, but look through the last few pages, Nordland has been communicating a lot about it there:
http://www.ulmf.org/bbs/showthread.php?t=27297&page=150