The big deal is that Tesla didnt buy Twitter, Musk did. Based on the Tesla engineers doing due dilligence on a non-Telsa acquisition seems like a conflict of interest.
Elon Musk has an obvious conflict of interest here. As CEO of a publicly traded company he has an obligation to act in the best interest of Tesla's shareholders. By using Tesla's engineers to look at his private company's source code he arguably doesn't act in their best interest, but in his own personal best interest.
I suppose there is a small conflict of interest as Tesla is paying some of its employees to do this work which doesn't benefit Tesla. As long as Twitter compensates them for this in some form however, I think this conflict is eliminated.
It's true though that a Tesla shareholder likely wouldn't want Tesla employee's focus to shift to Twitter too much I don't think.
Tesla shareholder here - in my opinion it's greasy, but realistically I know that most of Tesla's marketing happens on Twitter and having the platform running smoothly is in my best interest.
I suspect that kind of influence-peddling is how a lot of platforms like Twitter got a lot of sweetheart deals up to now anyway, so it being in the open is more interesting than annoying. The worst part is that it probably opens Tesla up to more lawsuits from 'activist investors'.