The plugin jail in 8.x is like a virtual machine of FreeBSD 8.x therefore you can install almost anything that you can install in FreeBSD. I say almost anything because there are some limitations or tweaks you may have to do in order to get everything working. But I personally have Nginx and MySQL installed into my Jail on FreeNAS 8.3.0 and as a test I have installed Apache/PHP Admin/MySQL. So you shouldn't have a problem as long as you don't mind installing and configuring from the command line. Oh and there are a lot of How to's on the forums for installing these ports.