I don't think the order matters, although personally, I would do the Recommended cluster first.
A lot of the patches in the J2SE cluster are also included in the Recommended, so you'll see some "error 2" messages when running the second cluster.
You can check the README files for both. They list the pacthes each cluster has.
http://patches.sun.com/clusters/8_Recommended.README
http://patches.sun.com/clusters/J2SE_Solaris_8_Recommended.README