Well, Kraft purchased half his father-in-law's company three years after he began his career there through a leveraged buyout. Presumably this was done with the blessings of his father-in-law.
I don't know enough about the history of Rand-Whitney to comment, but many of those mergers appear to have happened much earlier, under different proprietorship, and by the time Hiatt was in charge, he very likely owned a great deal of the company. Some of them were undoubtedly hostile takeovers, such as
this one (this article is quite unflattering to Kraft, who manages to slur working class Irish of South Boston and working class Polish of Montville, CT in one sentence).
Kraft certainly isn't the only person to benefit from starting his entrepreneurial career from a place of privilege, of course. Most billionaires, despite the Horatio Alger mythology, do so as well. This shouldn't be taken as a criticism unique to him.