I don't know whether there is any plugin available for Struts .. But you can build the struts application by setting right library in right directory..
Just build the new Web project and add the all the jars comes with the struts in to build path and Putting all the required xml files in Web Content/web-inf directory, you're ready to go..
To see How basic directory/file structure struts has, just download the "struts-blank.zip" from Struts site and un zipped it
As far as I know the only IDE with S2 support is IntelliJ, although I know the beginnings of an Eclipse plugin exist--the last time I tried it I didn't find it useful, but it may be more advanced now.