You are absolutely correct that you cannot simply select one group and have the mail app enter all of the contacts from that group into the "To" field. But that is not what I was trying to explain.
If you have 10 groups set up on the iPad and you want to send an email to all of the people in group #2, when you tap the blue + sign in the mail app in order to add more names to the email "To:" field, you can select Group # 2 from the contacts app.
Yes - you still have to add each contact one at a time that is in Group # 2 - I am not disputing that - but you do not have to sort through every other contact in Group 1, 3, 4, 5, 6, 7, 8, 9, & 10, just to get to the contacts in Group #2. All of those groups will not appear because you selected Group #2 from the contacts app already.
Its not what you wanted to do ... I realize that. I was just explaining what James was saying. You still have to enter each contact one at a time, you just don't have to sift through every group in the entire contacts app, since you were able to bring up Group # 2.
And yes this does work, because I have done it in the past. Like James, I have very little use to email to groups, but for the few groups that I did set up in iCloud, this works for my needs.