The issue isn’t a moral one from a a company perspective, it’s a conflict of interests issue.
Dating a customer and subordinate potentially undermines objectivity in customer pricing, customer chip access, promotions, performance, etc. That’s why it’s explicitly forbidden in Nvidia (and most companies) code of conduct
Why should we assume corporate codes are morally just though? I do not. In fact I would argue this is evidence that company codes are in a general sense draconian and/or disconnected from social reality under capitalism, etc.
this is like a theory and practice situation. in theory this is conflict of interest issue possibly undermines objectivity and so on. in practice Nvidia thrives and the man is a substantial reason of this. removing him will be plain stupid from the point of view of the company's performance.