This is coming soon in the first 1.0.0 beta (along with some other accessibility improvements). By default the tab order will not include the sub menus any more – only if you activate some sub menu via Enter. And you could also deactivate the subs again via Escape.
If you cannot wait for it, I can try to prepare some instructions how to backport it to the current v0.9.7 but you will need to edit manually the “jquery.smartmenus.js” file. Just let me know.