I was unaware that you were attempting to use Tessellation across multiple materials and then use those materials to be called upon based off of camera position. I was thinking of a shader that would act as a network to call multiple textures with one material assigned to the landscape. As you can only assign one material to a landscape this seemed to be the best option. I believe what you are attempting is possible through blueprints. Based on camera position you would call a certain material. Unfortunately, this way would require you to be a certain distance from the landscape itself, as opposed to a position on the landscape. For example if you moved away from the landscape and were a distance from the entire landscape this function would be called to change your material. If your character, or actor, were to exist on top of the landscape it would never reach that distance away and would not call the material. To answer your question, it may be possible, but it would not be a viable solution to what you are looking for.