My wife and I opened accounts, and we swiped our cards on each other's account. We did this with over $15,000, on each account with no problem.
Be careful through about using gift cards. I was trying to finish off a bunch of gift cards from the gift chain and I ended up swiping one of the cards several times because I forgot what was on it. The 3 or 4 declines trigged an audit about the multiple gift cards, they sent a list of 15 questions or so, and when I couldn't provide them the answers to their satisfaction, they simple shut down both accounts since "swiping gift cards multiple gift cards are against the T&C".
So I wouldn't worry about using the Authorized Users, but be careful not to get declined authorizations or using to many Gift Cards.