There is some note here
In general, you do not create accessibility elements for items in your application because standard UIKit controls and views are accessible by default. However, if you have a view that contains nonview items, such as icons or text images, that need to be accessible to users with disabilities, you create accessibility elements to represent them. In this case, the containing view should implement the UIAccessibilityContainer informal protocol and use this method to create an accessibility element to represent each item that should be exposed to an assistive application.
and here
The UIAccessibilityContainer informal protocol provides a way for UIView subclasses to make selected components accessible as separate elements. For example, a view might contain icons or drawn text that, to end users, appear and function as separate items. But because these components are not implemented as instances of UIView, they are not automatically accessible to users with disabilities. Therefore, such a container view should implement the UIAccessibilityContainer methods to supply accessibility information about these components to assistive applications such as VoiceOver.
I'm not familiar with Unity itself, but that's seems to be possible to hack containing view to support accessibility - you can build set of UIAccessibilityElemets
that represents currently visible items on screen.