When you create email and turn into an a/b test (right click on the email, select a/b test) does this format work for nurture programs? if not when is this useful?
Champion Challenger is for Emails and this type can only be added to Trigger flows or Engagement Streams.
If you use a Program nested in an Engagement Stream, then no, you cannot use Champ/Challenger. You should use the Random Sample flow step instead.