It's Nightbane actually:P
Netherspite is another boss that doesn't require summon
Someone told me summon wasn't required anymore but at least i couldn't find a way to summon him when i was there (someone else did, forgot to ask if he had done the Q) so not too sure but it's only one boss you can't do then:P
Just renember you need someone with key or a rogue with lockpick