No, it's a little different.
When an NPC node has a Response Menu Sequence, it will play while the response menu is visible. It will stop playing when the player chooses a response.
If you set the Dialogue Manager's Default Response Menu Sequence and the NPC node does not have a Response Menu Sequence, then it will play the Default Response Menu Sequence while the response menu is visible.
The Default Player Sequence will play when the player chooses a response, or when a PC subtitle plays. If the Default Player Sequence is blank, it will use the Default Sequence. (But if no PC subtitle is supposed to play, it won't use the Default Sequence either.)
Yes, you can use a {{shortcut}} in the Response Menu Sequence.