I got the Solaris net boot to work properly. I didn't change anything, but I did (a) reboot the boot server (channelling my inner NT admin) (b) run snoop on the intended victim. Now upgrading the server on a console line that eats several VT100 screen control characters, which makes for fun running a curses-based installer. This thing is supposed to be pushed into live ASAP too.
It annoys my inner Unix supremacist how many Solaris problems clear up with a theoretically gratuitous reboot. Unless it was the well-documented effect of the piercing BOFH glare.