How did the faa get veterans health records?
No idea, I'm a civilian. If that's the 'pilots claiming disability benefits from the VA and then holding commercial jobs' thing you're referencing -- well, that seems like a bigger fraud on the VA than on the FAA/CAMI, ie, more appropriate to claw back those cash benefits paid than to claw back the 2nd class+ medicals these guys were flying on.
...but even if the FAA grabs every pilot's tax records... what is OP's tax record going to show?
1099 for payment from Google or Youtube in some amount. Not 'cool flying videos', not 'clearly commercial flying operations lol', just general compensation, which OP can happily claim is from one of his non-flying videos, and what fed can prove otherwise?
If I run an illegal 135 charter, what are my tax records going to show?
1099 from Joe Customer or more likely Joe Customer's Company, Inc.
Or if I did it properly and I'm a corp also, there is no 1099, there is only a giant lump 'income' number, and the FAA will need to subpoena my bank records, trace the payments... it's a huge undertaking, and they need to do it for everyone they suspect. They're not equipped, funded, or interested enough -- particularly when they can just troll any airport hangar row and take their pick of violations to meet quota. (I do not believe they have this quota, just saying, why work hard and go all Erin Brockovich, when you can get the same thing by going to any airport and just looking around?)
If the FAA get every pilot's tax filings and some pilot set up an LLC called FAKE PLANE CHARTER LOL EHRMAGERD, LLC , well, they sort of were asking for it. But those company records are already public, and the problem of 'proving it' still exists. The tax returns add nothing actionable.
I can't think of a single thing in an IRS tax form that directly indicts a pilot for breaking FARs. Maybe I lack imagination here. Even so, I still think OP's scenario with the IRS has nothing to do with the FAA, as the puny little potential violations of FAR that could be argued -- they're in the past already, so he should focus on the present and minimizing tax liability payable.
$0.02