Commands: No, they did not work - I only found them as the (chronologically) latest potential solution to my problem. Ticked off.
The PiHole docker is on its own separate IP. However, according to the video howto, it still requires port 80 on the Unraid machine. So I changed the Unraid http port to 8008 using the GUI last night. Unraid rebooted without any hassle after that and I could start the array.
Line in "go": No idea either. Didn't touch it ever. Don't know what it's been doing but it's been sitting there without doiung any harm so far.
Edit: I'll be damned - it worked, the GUI is back up. The "go" line made no difference; it was the port. I don't get it - why can I change the port then?