Each Yeoman generator, when installed, makes available one or more Yeoman commands. On the command line, you don't run a Yeoman generator, but a command provided by a generator. To make that distinction, the user interface of the Yeoman wizard has been changed a bit:
A generator that is available without having been installed is iconized by means of a green download arrow. When that icon is right-clicked, an Install action can be invoked, which will run "npm install -g generator-xyz" from within NetBeans IDE. Once that has been done, the "yo --help" command will be run again, automatically, to populate the upper view with the newly available Yeoman commands.
When a Yeoman command is selected and Next is clicked, the Yeoman command will be run, via "yo ko:app", or whatever the selected command is. Then the generated application will automatically open in NetBeans IDE.
From the above, it's very clear what the biggest advantage of Yeoman integration in NetBeans IDE will be: anyone will be able to browse through (the lower view above has built-in search and filtering features) the available generators and pick the ones they'd like to use directly in the place where the generated applications will be developed.