My favourite thing when visiting my Dad in Guangzhou, you can have Dim Sum at midnight, its amazing, if you can somehow find a place that serves late Dim Sum over there do it, its almost as amazing as having McDonalds breakfast at 1AM.
Also I've never had a problem with vegetarians and Dim Sum... They usually have a decent vegetarian selection, though you sometimes have to order it separately so that might be the problem, but if your at a legit Chinese place just ask and they usually have tons of tofu disks and vegetable dishes to order and maybe even zhai (Chinese imitation meat stuff that actually tastes good, I'm a meat lover and I still eat it all the time).