I had a feeling it was Giuliani who was distorting the facts in that case.
Yes, he hired a company to work on (or at) his house that later turned out to have hired illegals (this is according to CNN's "fact check afterwards". I've read it other places too). I don't think Romney ever denied it. I do think Giuliani looked really bad because he had nothing when Romney turned it back on him and asked if we should demand papers for everyone working on our house. That was the only good line Romney had all night in my book.