no idea. I'm actually a noob. I've learned just enough to download, trim, and check the stuff that I own. I figured if I hacked the system it would be yet another system that I don't play. anyway, I'm sure they do some sort of check. I had to send in my original switch to be repaired. it would turn on (sometimes) and show the nintendo logo, then power off. nintendo said it was nand corruption. if that was the problem, they may not be able to tell if it's been tampered with. it was still under warranty, and they sent me a refurbished system. it wasn't the same system, and funny thing is that it's not patched some five months after the patched systems started appearing. I've had this new switch for about a year now, no problems with it.
edit: and by check, I mean verify they're safe without malicious code and they're complete. I've had several nca corruption errors with some of the stuff I've gotten from the dark site. as it turns out, some of their games have parts cut off somehow.