Congee Village has about 16-17 Vegetable dishes, including 2-3 with Dried Scallops or seafood. Chinese restaurants typically use chicken broth (and/or with beef or pork bones) in their prepared dishes so hopefully your vegetarian friend won't mind. Otherwise for a guaranteed meat-free experience try the Vegetarian Dim Sum House at 14 Pell Street
chinese seasonal (water) spinach with bean paste is one of the best things on the menu. vegetarians i've eaten with have also been very happy with the braised bean curd casserole. kind of a shame to eat there and not be able to try the more exotic offerings, but i'm sure vegetarians are used to that kind of thing...