Google-groups – How to remove the red “Google Groups will no longer be supporting the Welcome Message feature” from the Google group

There does not seem to be a way to disable those emails, as long as you have the moderator permission. What you could do, is ask the group administrator to create a new role which has all your current permissions, minus Approve messages. That way, you should be able to do most of the things you can do now on the group, but you will not be able to moderate messages, and you will not receive those emails.

Ask the moderator to go to https://groups.google.com/forum/?fromgroups#!managemembers/[your-group-name]/creategroup to set up a new role, and refer to the documentation.

The option to directly add members to a group is indeed available again.

They had removed it due to spammers misusing the feature: http://groups-announcements.blogspot.com/2011/07/new-in-google-groups.html (July 2011)

Spam improvements: Starting next week, we will remove the option to “Add members directly” to googlegroups.com groups since spammers have unfortunately abused this feature. Group owners will still be able to invite you to join their groups and you will have to accept their invitation before you start participating in and receiving messages from the group. Learn more here: http://groups.google.com/support/bin/answer.py?hl=en&answer=46373

I guess they made the option available again due to user pressure and by introducing or strengthening the confirmation code to avoid spammy use.