No, that's incorrect. Y!G does have a NuM feature and it's the same as GIO...it's in the group settings, not the subscriber settings. See attached screenshot.
No, that too is incorrect. ?
Yahoo groups has a like-named feature, but it doesn't work like Groups.io's.
In Y!groups the NuM setting is only a group-level control, there is no corresponding Posting Privilege. Which means that in Y!groups new members only ever get unmoderated by a manual action of a moderator -- changing their Posting Privilege from the Moderated override to (hopefully) use the group setting.
It also means that in Y!Groups there's no way to distinguish a member who is moderated "for cause" from one that is merely "new". The moderators must keep track of that by external means.