Hello,
From what I understand, Ubuntu doesn't support nested group membership.
However, after joining the system to AD, all you should really need to do is reference an AD group in your sudoers file and make sure your users are members of the group. For example, in your sudoers file you could do add a line like the below where <AD_Group> is the name of your AD group. Before adding the group, make sure the command "adquery group" is able to return the group.
%<AD_Group> ALL=(root) ALL
Here's a good guide I came across on the Ubuntu forums that discusses sudoers configuration that may be helpful.
Regards,