Cardio training helps you to reduce your body fat and wheight, which is defenitely advantageous for this surgery. It also increases your overall bloodflow, this way nutriens and other cell components which are needed to fill in the bone gap can get to their destination faster and easier.
I'm not an expert but being in a good shape is generally beneficial for this surgery (and baiscally in every other aspect of life too).
Doing cardio will also not result in big muscle gains on your legs which would make the streching process harder and more painful.
