This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
Ofcourse you can, if you make a class that extends Thread and implements Serializable, you can serialize objects of that class. The article you refer to doesn't say it's impossible to serialize an object that extends Thread.
But it doesn't make much sense to serialize a thread-like object. Serialization makes sense for classes that are containers of data, not for "live" objects like threads, sockets etc.