Probably. As far as I know, only DOM elements with a tabindex attribute get keyboard events, and you probably don't have any of those in the rendering of your tiddler.
I've also been experimenting with similar keyboard shortcuts, and I got it mostly working. Head over to
http://nome.github.io/TiddlyPlugins/ and press F2 to edit a tiddler. You can't select the tiddler to edit with the mouse though, you have to use Ctrl+Up/Down. It's still a bit rough, and behaves weirdly sometimes, but the basics are there.
Cheers,
Knut