You really think the likes of Musk and Bezos can't sleep at night because of risk to their careers? These guys don't worry about credibility because they make their own credibility. This is more of a position of "I'm a captain of industry, if the President wants to call me to ask a question, I'll take the call". Doing so is both good business (good for their businesses at least), and is compatible with a position of "this man is not qualified for the job", because "that's why he's got me on his advisory board". If anything, it's a subtle, shrewd move on the part of Musk.

It's a lot more mild than the statements made by politicians to whom Trump has granted substantive positions.