I doubt feeding raw food has anything to do w/ worms, maybe if it is bad meat (road kill or something), but most likley if worms are present it is due to contact w/ another dog or dog area (hook, round & whip worms) or eating rodents & fleas (tapeworms).
Tapeworms very rarely show up on fecal exams, hook, round & whip worms show up about 65-80% of the time. Remember that a fecal must be done right. No excess heat or light & No longer than 1/2 day refridgerated, the fresher the better.
I believe there are maybe a couple/few other types of worms but they are more rare & can not remember.