Free demo games in Facebook apps allowed?

I noticed a good couple of FB apps lately that are embedding free to play slot games in an iframe and offering it as a Facebook game. Although I know it's just play money I have been wondering if it's not against facebook Terms of use as these apps often include an affiliate link to an operator.
Here's an example I seen recently:
https://apps.facebook.com/the-avenge...debar_bookmark
The affiliate is promoting casino.com and bet365 within the app
https://www.gpwa.org/forum/images/In...W4f2C1DNMAY%3D

The app and its corresponding page (https://www.facebook.com/avengersslotgame/) has 5.400 likes which is quite nice results and I assume many people use it.
Is this form of promotion actually legit and allowed on social networks?

please share your views and thoughts
thanks