Four years later, a local writes
;) I answer in covid time (now we are under curfew 10pm to 5am) but what I write applies in general.
Short answer: no, no traditional food in Bologna after midnight.
Proper restaurants close at 10.30pm or 11pm and, yes, very possibly the kitchen closes sooner. After midnight not even kiosks are reliable, out of the “nightlife area” within the city center.
I found some of the page linked in the other answer on a web archive. Some of the venues here listed are discos, pubs or bars. Altotasso is a late night drink place, not really a late night food place; after a certain hour in the evening, you will only get sandwiches and snacks. Arterìa is great to “meet new people”, not really to eat something.
If you are ok with pizzas and bakery products, Gingio is next to the two towers, only closes 6am to 9am and has saved many lives.
The latest night tagliatelle that you can find in town are probably served at Dragon Pub in via della Repubblica. Here you can find proper quality meals with first and second courses…say till 1am or 2am.
Among the proper restaurants, Il Rosso claims to close at 11pm but, I bet, they would serve you food at 10.45pm.