So one, I don't think you know what the word "impostor" means. If somebody faked your wife's identity, I think you could be reasonably upset even if she could "do the job" adequately, and it would be weird indeed to say she wasn't an impostor.
But two, are you serious with "If they couldn't do the job they would've been fired"? I think the most charitable assumption I could make is that you must not have been in the working world long. There are plenty of places that are bad noticing and getting rid of underperformers, even when everybody involved is well meaning. If somebody is actively running it as a scam, it could be hard indeed to detect. And really, they don't have to evade detection forever. Even a few months of paycheck may be more than enough for them to cover the costs of getting the jobs.
But two, are you serious with "If they couldn't do the job they would've been fired"? I think the most charitable assumption I could make is that you must not have been in the working world long. There are plenty of places that are bad noticing and getting rid of underperformers, even when everybody involved is well meaning. If somebody is actively running it as a scam, it could be hard indeed to detect. And really, they don't have to evade detection forever. Even a few months of paycheck may be more than enough for them to cover the costs of getting the jobs.