You can easily add vertical snippets in 1SE. The process is the same as adding a horizontal snippet, but your videos and photos taken in portrait mode won't have bars to fill in space.
To create a vertical snippet, tap on "Fit to Frame" in the mashing screen and select the "Portrait" option. Then, tap on the blue checkmark button to save your changes.
Shot in portrait mode
Shot in landscape mode
You can easily see how your snippet will look like in both orientations by tapping on the "Rotate" button on the snippet selector screen.