Spent the greater part of the day getting matrices and \mathbb to work on my FreeBSD/MediaWiki install.
The issue is with amsfonts. I installed the latex port, but this does not include amsfonts. Deinstalled and installed teTeX, restarted apache and voila I now have vectors, matrices, and more.
to see some matrices and \mathbb's
I posted what I did in some detail to:
JS Wiki Mediwiki
MediWiki Manual: FreeBSD