Does Gravity Forms create a post type and are they shown in a standard type of WP post edit admin page. If yes then you can set the field group location to this post type and that should work, unless GF skips the use of the WP admin page.
Another options would be that if GF has any way to add to or alter the admin page so that you can insert additional fields inside of the form that they use. If this can be done then you could use acf_form() with ‘form’ set to false to add the fields.
Worse comes to worse, you could modify the GF admin page code to use the acf_form(), but this would not be a good idea unless you want to redo these changes every time you update GF.
