Aweber requires confirmed (double) opt-in for 3rd party integration such as with WarriorPlus. However, you can email their support and ask them to make an 'exception' for a list to allow single opt-in, and they will often make the exception for you.
This must be done for each list you want them to change, it is not done for your entire account.
Note: It is not guaranteed that they will make the exception, but they often do.