Many times, just like there is not one cause for depression, there is not one cure either. Most people find that exploring myriad treatments in succession or together results in a treatment regime that works for them specifically (e.g. dancing + meditation + dietary change + acupuncture + certain drug = happiness for someone)
So yes, Chinese Herbs can be part of a successful depression treatment regime. However, TCM practitioners would rarely (if ever) prescribe 1 herb in isolation to any given patient, or the same combination of herbs to many different clients. Instead, most Tradition Chinese Medicine (or 'Oriental Medicine') practitioners come up with an individualized 'tincture' or combination of herbs to specifically treat their client's particular depression symptoms. For example, if one depressed patient had weeping episodes, trouble with low energy, and digestive issues, they would be prescribed different herbs than someone whose depression was exemplified through the symptoms of insomnia, anxiety and anger.
Additionally, a TCM practitioner (the person prescribing the chinese herbs in most cases) would also be working with the patient on dietary changes, sleeping patters, and perhaps performing some acupuncture as well. Therefore, the ability of the herbs to treat the condition is difficult to measure as they are a part of the entire treatment regime.