The key is whether or not Twitter is compensating Tesla (and therefore its shareholders) at a fair market value for the time and resources used by Tesla employees for the benefit of Twitter (and therefore Musk as its owner). Not whether or not it makes sense to do so.
If its a dumb idea on Twitter/Musk's part but Tesla is fully compensated for their engineers' time, all is OK.
If its a great idea but Musk just assigned Tesla employees to do work that does not benefit Tesla and does benefit another company that he owns, that is an issue.
The scale of this is irrelevant. Absent fair compensation to Tesla, even one employee doing a day's work for Twitter is prohibited self-dealing. No one would bother filing a derivative suit over such a small amount, but SEC penalties could absolutely apply afaik.
If its a dumb idea on Twitter/Musk's part but Tesla is fully compensated for their engineers' time, all is OK.
If its a great idea but Musk just assigned Tesla employees to do work that does not benefit Tesla and does benefit another company that he owns, that is an issue.
The scale of this is irrelevant. Absent fair compensation to Tesla, even one employee doing a day's work for Twitter is prohibited self-dealing. No one would bother filing a derivative suit over such a small amount, but SEC penalties could absolutely apply afaik.