When it comes to research about paradigms like that it's hard to evaluate them. If you look at nonviolent communication and set up your experiment well enough I think you will definitely find effects.

The real question isn't whether the framework does something but whether it's useful. That in turn depends on your goals.

Whether a framework helps you to successfully communicate depends a lot on cultural background of the people with whom you are interacting.

If you engage in NVC, some people with a strong sense of competition might see you as week. If you would consistentely engage in NVC in your communcation on LessWrong, you might be seen as a weird outsider.

You would need an awful lot of studies to be certain about the particular tradeoff in using NVC for a particular real world situation.

I don't know of many studies that compare whether Windows is better than Linux or whether VIM is better than Emacs. Communication paradigms are similar they are complex and difficult to compare.