FOR FREE sure. The addons can not be charged for period. Not at all. Never. Not in any phase of development. If someone is working on something privately with friends who have free access that is one thing.
If people can join their group via paid methods to get access, then that is a paid version. Being Alpha or Beta does not matter. You can’t charge money for addon access period.
It is a very good way to get on the radar of Blizzard’s lawyers in a bad way.
There is no exception to the rules just because something is being called Beta or Alpha that allows them to charge for access.
The rules were already linked in the beginning of the thread.