At the tactical level, the embedded cultural experts should provide a useful means through which soldiers can engage locals and respond to their opinions, wants, needs and concerns. The mere fact that the Army is trying to address the concerns of locals and work within their cultural context will help the counterinsurgency campaign.
However, HTS also has a lot of limitations. It is not going to provide unbiased information. The Census Bureau has a hard enough time getting decent response rates in the US Census, and its going to be even harder conducting surveys in extremely rural, underdeveloped warzones. The places that are the most violent are the ones where this information is going to be the most critical, but they are also the places where it is going to be the hardest to collect accurate information.
HTTs (Human Terrain Teams) are also going to be very vulnerable to information tapping by other components of the military and intelligence communities. According the its website "HTTs [Human Terrain Teams] do not collect actionable military intelligence, nor do they participate in lethal targeting", but I find it hard to believe that HTTs, having spent so much time on the ground talking to locals, will not have gathered some actionable information. The mere possibility that HTTs could relay information to other military units may impede their effectiveness.
Finally, there is only so much that cultural information and public opinion polling can do for a counterinsurgency. If done properly, HTS is definitely going to help legitimize the Army's actions, and in that sense is absolutely vital. HTS is going to tell soldiers what they can do to gain the trust and respect of the locals, but its not going to provide the Army with any information that will fundamentally change the counterinsurgency. Afghans want a legitimate government, minimal corruption, security and economic prosperity. HTS isn't going to actively accomplish any of those objectives, all it does is improve the Army's ability to accomplish them.