I had once a similar problem with a bad patch zip file and I finished up using the .jar file from the signed patch to install it, although I've informed them to replace the bad zip.
So just for curiosity, I've downloaded the s8containers-bundle-solaris10-sparc.tar.gz in a sparc box running Solaris 10 5/08, extracted and followed the instructions in the README, i.e for my Solaris 5/08:
pkgadd -d `pwd` SUNWs8brandr SUNWs8brandu SUNWs8brandk
and it complained because SUNWs8brandk wasn't in the current directory. I think it's a "usual" Sun documentation error. They meant to write SUNWs8p2v instead of SUNWs8brandk and to confirm I did a little search and came across this wiki
that confirmed my thoughts...