You may want to use Return or Enter when writing in iChat, for example. They are not in the Gestures list.
The "Vertical Space" gesture inserts a Return character. You may use it anywhere that Return or Enter might normally be required. In iChat, for example, this gesture will send your message.
It is possibly, though unlikely, that your application may distinguish between the insertion of a Return character and an actual keystroke. In that case, the Vertical Space gesture may not work. You could assign Enter or Return as a keystroke on one of your pen's buttons to achieve this effect. This is done in the tablet setup software, such as the Wacom Tablet application.