Incorrect. If brand-name manufacturers had this sort of power over generic drug approval, then there would be no generic drugs. The people who are saying that they can withhold consent to having their drugs used in bioequivalency trials are doing so based on a court case that never went to trial, about a company (mis)using REMS (a restriction placed by the FDA on certain dangerous drugs) to keep other companies from having their product. Daraprim is not a REMS drug AFAICT.
The real reason why there are no generic versions of Daraprim is because creating one and getting one approved costs a lot of money. When Glaxo was still selling the drug at a relatively low price, there was no incentive to make a generic because said generic couldn't be competitive. Now that Turing has marked the price up, a generic is far more feasible, but it will still take a considerable amount of time before one gets on the market. And even then, it might not be worth the risk that Turing will just lower the price and undercut any would-be competitors.