[wurzel]

I think you can always use the IP stuff in your campaign if you own the books. The HL editor offers enough capabilities to recreate the missing parts. You simply must not sell the stuff if you use the intellectual property which WotC did not include in the SRD for some reason.
If you want to share your self-developed implementation for HL check out your local laws. I think in Germany you may do that since the IT-implementation carries just the names, but more than 90 percent are not WotC IP but your own.
If the names happen to be a problem, simply call the mind flayer a FFN ("fiend with four noses") and similar replacements and you're done.