From the sounds of it this is not a case of pirating his book. Its a case of someone using stuff from his book in a wiki. But copying chunks verbatim.
That is semi-common with wikis. Not all but I've even seen it done on wikipedia.
If it is just being used for reference and database then going after them will come across poorly, or very poorly as noted above.
Now if they are misusing the material in some way then its perfectly fine to go after them or at the very least request they change it to be more in like with the source.