Let me begin by saying that authentic dim sum should not be pork free. Although not every dish in dim sum restaurants contains pork, the iconic ones such as char siu bao and siu mai are traditionally made with pork. So when you substitute the main ingredient with something else like chicken, you have distorted the intended tasted.
But since we live in a multi-racial country where everyone loves dim sum, there is a demand for halal and pork free dim sum restaurants, especially in KL. Among them, Oriental Chinese Cuisine in Pullman Kuala Lumpur Bangsar is one the few good ones which I would recommend.