Flax oil isn't magic by any means. It's simply an essential fatty acid that most dieters are deficient in. To lose bodyfat optimally you must have all of your body processes running smootly. If you are deficient in EFAs, thus your body isn't functioning optimally, then flax oil can definately help you. However don't expect to just start dropping fat magically by taking it, it's not like T3 or DNP by any means.
It's also not required to lose weight. If you are getting plenty of fats from sources like peanut butter, nuts in general, olive oil, peanut oil, fish, etc.. then you probably aren't deficient in EFAs. Flax oil is just a supplement to get them without worrying about it. People drink protein powder because it's hard to get enough protein from food alone. Same goes with EFAs.