Uncle Vanya in Red Sparrow is a manipulator. And I was under the impression he always wanted to have some "action" with Dominika. That's clearly why he prostitutes her through the sparrow program.
That was quite lucky for him that not only did the correct circumstances happen that he can ultimately blackmail her into the sparrows. But more 'luck' was the fact that he happened to be able to tap that one phone conversation to change Dominika's spirit, and give her a taste for blood.
But was it luck?
The accident that cost Dominika her dancing career, that started all the movie's events, was caused basically because the dancer had sex with the second ballerina, and that the ballerina was able to convince him to assault Dominika. That needed some kind of persuasion. Not just a pretty face and soft body (I don't imagine the first dancer at the Bolshoï having difficulties finding willing pretty women).
Placing a spy at the Bloshoi is some hard work, but I can see it bear result long term (at least as long as you don't sacrifice her hoping to shag your nephew), After all the first assignment of Dominika was because she was a dancer.
Do we have any clues (inworld or outworld) that the second ballerina was indeed a sparrow and that she acted at the explicit demand of Vanya?