Well that was a heck of a reply someone gave you.
Fear aggression for me is so easy to spot. Some cases are mild and some cases more severe. On any note, I would not own a fear aggressive dog and I feel the best thing for it is an early grave. I don't have the time nor patience to modify MY daily life for a dog. I am also in a position I have to consider the safety of my children. Either it fits or it don't. I also don't believe in rehoming cases like this because so many idiots think they can save the dog, help the dog, etc and in the end something terrible can or may happen due to letting down our natural guard over time. Ok so that is my OPINION on the matter.
To get down to your questions. Yes, some dogs can be mildly fear aggressive, as in, they react only in certain scenarios that are perhaps very scary to the dog. Working in the vet clinic, there were some dogs that came in that due to fear...they would lash out at us. However, in at least a few of the cases for sure, I knew the dogs really were trusted family companions. They did still display a slight weakness but to me, that can be overlooked with the right owners. Then there are the dogs that are afraid of everything. They hid behind the couch and snarl when company comes over, they avoid eye contact and if it is made they scream, may urinate or defaecate themselves and lash out. This dog will walk around with the tucked tail and is always on guard while being overly cautious of everything around it. Nothing in this dog mirrors confidence in any way and the list goes on. This dog when confronted, scared, pushed etc, will lash out. This type of dog needs to be destroyed without second hesitation. (my opinion of course) But they are dangerous and unpredictable. The thing with a fear aggressive dog is...they lash out without warning. You know where you stand with a dog that has aggression that is NOT fear motivated. However with a fear aggressive dog you have no clue what slight thing may trigger a reaction and it can be so fast and so profound you still haven't a clue when it is done and over with.
NO a fear aggressive dog will NEVER become stable. It will NEVER be a normal dog. I don't care what sort of recondition is done. The dog can never be trusted. Its environment can be modified but that simply hides the underlying problem. At some point, as I mentioned above, due to human error, laziness, or what have you, the human will fail the dog in this scenario. Now, my word of caution here does boil down to genetics. I have seen, first hand, dogs that appeared to be fear aggressive at first glance. However, it was due to horrendous mistreatment. The difference is...after a mere couple of weeks of GOOD treatment (without pussyfooting around it) the dog will make a complete turn around.
I have also seen weak nerved puppies. Simply weak nerved and not fear aggressive persay at this young of age. BUT you take this weak nerved pup and place it in a very domineering household and you could have issues with fear aggression coming out. On the other end of the spectrum, you place this pup in a very laid back and coddly household and you could also have issues. This type of household oftentimes "rewards" the pup in certain ways for displaying uncertainty...a monster can be created. Yet, placed in a normal assertive household...this same pup will probably mature to be a half ways decent family dog. But puppies are different as they do have developmental phases and the upbringing of them can make or break pups with certain personality flaws. This is given the fact that not all dogs are born perfect and pups are moldable to a certain degree. You take a puppy who was born with flawed genetics that predisposed it to being fear aggressive, raise it in the wrong household initially...and jump that dog from home to home...there is no fixing it in the end. Personality is cemented. The behavior has become learned, relied upon and a way of life for the dog. Just like in human psychology they say our personalities are fully formed and cemented by the mere age of 3yrs old. Until that age...there are ways of swaying the genetic predispositions thru the environment of which they are raised, be it good or bad.