Yes to all of this.
That being said... I feel like there is an attitude here on this site where “if someone else does something I shouldn’t touch it”. I’m not saying it’s enforced, just that it’s something I heard quite a few times and I think it’s taken too far by some. Don’t get me wrong, some mods fill a niche need (animal farm is a great example) and making another mod of only versions of it could be considered bad form. But even then it doesn’t mean that someone should feel they shouldn’t make animal farm plots in their add-ons if they have an idea.
And Vault-Tec themes plots isn’t a niche thing or “someone’s thing”. It’s a Fallout thing. There is no reason why every mod author shouldn’t make rooms that fit that look. Besides, if we asked uituit, tinuvia, RobotSmells and sirlach to design a vault tec add-on, I guarantee we’d have some very different designs. For starters expect a lot more blood from uituit, sirlach to be efficient in space, RobotSmells to have some weird unique twist mechanically and tinuvia to have unique different twists.
Not saying it’s a good idea to have them do it, not sure we need four vault tec themed add-ons. But my point stand that as long as it’s a creator spin and not just doing the same thing, doing something in the same theme or similar to what someone else is doing doesn’t need to be seen as a no-no.