Some perspective.....
There is no good data to give numbers on prevalence of tension pneumo in trauma. There is some data regarding TP in inpatients secondary to other lung pathologies and/or surgery. One article in the Journal of Emergency Medicine stated that in pre-hospital trauma a probability of 0.3% may be inflated, and that number came from a study from the Vietnam war.
In order to have a tension pneumo, there needs to be something going on to the pleura around the lung, and the lung itself, and it must be closed (well, not in every instance, but the vast majority). So, open chest trauma usually (but not always) will lead to a simple pneumo and not a TP. When you seal the holes, then it can most definitely become a TP.
The signs/symptoms (s/s) of a TP, while very specific, are also often very subtle, and very difficulty to pick up in the field in the best of circumstances. If you needle someone who doesn't have one, and unless you pierce vasculature that lies immediately below and parallel to the rib, the worst thing that happens is causing an open pneumo. Easy fix, you get a chest tube.
Bottom line: the probability you will encounter one is extraordinarily rare. The probability you see classical s/s is rarer. Don't needle if you haven't had the training, and if you have had the training, be sensitive that you may be liable for any damage.
Would I do it to a vic of a GSW, or a vic of a MVC? I have been in the medical field in some capacity since 1990, a paramedic/flight medic, a FMF corpsman, Enroute Care Nurse, TCCC instructor, ED nurse. Unless I see the most obvious signs AND I know EMS would be delayed, no.