https://us.forums.blizzard.com/en/wow/t/ui-add-on-development-policy/24534
Not the EULA … but at the top of the UI Add-On forum is policy… there is a post blue that clearly states:
“1) Add-ons must be free of charge.
All add-ons must be distributed free of charge. Developers may not create “premium” versions of add-ons with additional for-pay features, charge money to download an add-on, charge for services related to the add-on, or otherwise require some form of monetary compensation to download or access an add-on.”
Of course, it’s up to Blizzard how they wish to interpret and enforce this. It’s an easy argument to make that a data service is monetized in the addon.