Add user picture to profile 2/any entity for that matter...
You have two options.

You can use theming to make whatever you want use the profile picture.

Another options would be to add the picture from the profile to the user object on load.

Third option would be to sync the user picture with the profile picture whenever the profile entity is saved.

If you want it to take effect everywhere, you need to use the third options, which adds the headache of having the same data store twice and the problems such a thing can bring,