I would say no. undefined class will not get blocked. I believe you need to define the class and tag the file so your DLP rule can kick-in with the action. Please provide more detail on what your looking do too.
Thanks for your anwser.
The undefined device lcasses list is about Smard cards and Smart Card Filter. Our customer uses smart card and they say, sometimes it works and sometimes not. And i thought that this could be the problem. But I guess this is an other problem.