A hastily deleted but still cached blog post says "yes".

Chris Matthews then yells, (literally yells - out fucking loud, and mind you, this photo shoot is going on in his MSNBC studio where he films his show which made it funny - photos to come...) "I will not be in the same fucking picture as Arianna Huffington!! Not a chance of that!" He goes on some other rant about her which I didn't catch because I had to walk away, laughing. As I'm walking back to set, he then storms back out of the film studio room where his show Hardball is filmed. But actually as he's walking out, he turns to me - probably because I was laughing and says "I want you to know that she hired a Private Investigator to spy on one of my colleagues; someone in the media." Tucker walks in at that point and I'm literally writing down what he just said on a paper towel so I'd remember that quote. Oh yeah, so Tucker walks in and says, "Yup, he's right, she did hire someone and nobody really talks about it, but I really like her so it doesn't bother me."

h/t Jossip

UPDATE: Maybe this story explains why Tim Russert banned Huffington from appearing on any NBC-affiliated show to promote her book. Last month the story was that Russert had banned Arianna because she said unkind things about him. That never made much sense. That Russert is steamed over something like her hiring a private investigator to watch Russert makes a bit more sense except that Arianna denied it years ago. It's all so muddled even Nick Denton is confused.