This sort of thing def happens online. But in very large player pools at the lower stakes, it goes mostly unnoticed. Though in the abstract, playing on another player's account to gain an advantage is cheating IMO (I don't think this should really even be an opinion).
Imagine a known fish/whale sitting down in your live game being told what to do by someone of clearly superior skill via earpiece and eyeglass camera.
At the higher stakes where the player pools are very small, almost everyone knows each other, and integrity counts for a lot, this is a pretty big deal. It's not Mike Postle levels of craziness, but in a small circle of people where reputation can mean everything, this is pretty bad.
You can say this comes with the territory of playing online. That's true. But that doesn't make it any less of a cheat. Just one where it's hard to get caught in large player pools.