They have a clear monopoly on the talent in MMA but it would be impossible to argue that they have a monopoly on the business of MMA. They haven't got set ups in every country in the world, on every channel and roster of every fighter. It is impossible to say there is a monopoly.
The purchase of Srikeforce wasnt deemed that way but it doesnt mean that the UFC isnt a monopoly and doesnt mean that they wont revisit or or that there isnt another ongoing investigation on other UFC business practices. From what we know, the UFC is still being investigated in other areas.