To follow up on my own post of a month ago: I just build Mediawiki in a Solaris 11 zone, with no real problems. I built the SAMP server using this page from Neal Pollack of Sun:
http://www.sun.com/bigadmin/features/articles/samp_setup.html
This used Solaris Apache, mysql5 from blastwave.org, and php5 from php.net. Once PHP and mysql were talking, MediaWiki worked without any modifications.
I started with a "small" zone with a local loopback-mounted /usr/local and shared /usr, /var, and /opt. I built SAMP in the global zone, but had to rebuild libxml2 and reinstall PHP on the client zone to get all the right libraries in the right places. Reinstalled PHP the quick-n-dirty way with gmake -i install, to get the right things written to /usr/local . Of course PHP was otherwise identical in the global and client zones. I would not be comfortable doing this on a customer-facing production server so I am going to rethink this.
Next up: security tightening, and probably php cacheing.