The Clinton campaign is gaining credibility by lining up moguls that support her. This shows she is not anti-business, particularly since these supporters traditionally vote Republican. It is an even stronger message given Donald Trump's business experience. The support shows Trump is seen as a dangerous person that is not competent to hold office.
Hillary Clinton's campaign does not gain more credibility by having mogul after mogul proclaim, "I'm with her." Instead, Hillary's campaign needs to focus on policies that will connect with Middle Class voters that have been struggling the past decade. Many Americans face stagnant and declining wages, which result in diminishing economic opportunities. Hillary needs to articulate a message that can change the economic conditions for the Middle Class. This will provide her with more credibility.
No, lining up mogul after mogul does not give Hilary Clinton's campaign more credibility, however, it does make it seem as though she has a better chance of winning the election. Although gaining the support of mogul does not make the Clinton campaign seem more trustworthy, it does seem to be a stronger campaign because of it.
What gives Hillary Clinton credibility are her actions and track record, not the celebrities or moguls she influences to support her. This applies to any candidate running for President. Supporters can be bought and promised favors, but it is a candidates actions and track record that are a better indication of their credibility.