mdworker not running

Reinstall the server OS.

I'm not aware of any way to selectively install Spotlight's required components. Also, I don't do server stuff, so you'll have to await for one of those gurus to pop in. Good luck.

Hello. I found myself with the exact same problem. My solution which worked for the moment was to use onyx and for now it works again as expected. Maybe that could help you.

TL;DR: Check the console logs for errors.

Spotlight isn't specific to OS X Server.

Reinstalling OS X and OS X Server isn't a huge project and is a common solution for some variations of "weird" but wouldn't be my first choice here.

I'd start with a look at the console log files first and see what (if anything) is logged there around mdworker et al.

I've seen cases where odd-ball or corrupted files can trip up Spotlight, though finding those files can sometimes be a little interesting. If it's a user's file that's tripping Spotlight, reinstalling OS X Server doesn't help.

Later versions of Spotlight tend to work a little better, though I'm guessing there's a reason you're still at 10.6.8.