The styles for the arrows are at the top of “jquery.smartmenus.bootstrap.css” (the “.sub-arrow” class). Though you will need to play with them quite a bit to achieve something like that.
Plus in the current version of the Bootstrap add-on the default Bootstrap behavior is honored and it doesn’t allow to separate the behaviour of the arrow from the rest of the menu item – i.e. use the rest of the item for link and the arrow always for sub menu toggle. The default Bootstrap behaviour is to use the whole item just as a sub menu toggle. This will probably be changed in the next SmartMenus release and what you gave as an example will then be the default behaviour for the SmartMenus Bootstrap add-on but at least for now, it’s not.