Alright, lets give this a shot.
Lets write down a chain of how reality is perceived before we start. That way, we can understand where this question lies on the spectrum of experience.
The fundamental nature of reality of an unenlightened being is described as thus:
- Nirvana exists.
- All experience is born through Nirvana.
- Experience is conceptualized as a false self. The illusion of consciousness is created.
- A false self "observes" the same experience in item 2.
- All "non-self" experience is conceptualized.
- Conceptualized experience is labeled as an "existent" or "non-existent".
I believe that it must be considered an existent as it is known by a directly perceiving mental consciousness. The same can be said of a face in the mirror although in this case it is directly perceived by the eye consciousness. Is this true?
Consciousness is an illusion, and therefore, I disagree with your belief. Consciousness is a part of the illusion of a separate, permanent self. If I understand your definition of "existent" correctly, then I would say anything you directly experience is considered an existent, with the exception of Nirvana. Nirvana can not be experienced, but it can be realized. Therefore Nirvana is an existent.
I posit that a dream snake and a snake I perceive in waking life are both conventionally existent.
Yes. There is no difference in how our "waking sight" and "dream sight" operate. Both are nothing more than experience coming through our 6 sense doors. Anything that is experienced, is an existent. You can see, hear, feel, taste, and smell both a dream-snake and snake. You can not directly perceive the son of a barren woman through sight, sound, taste, touch, or scent, but you can conceptualize about the son of a barren woman. You can experience thoughts about the concept of a son of a barren woman. These thoughts are absolutely an existent.
Further, that neither are ultimately existent. And that neither are real. That is, they are both equally unreal. Is this true?
What you are observing here, if I understand you correctly, is what is called emptiness. All experience is. No experience has any qualitative aspects. No experience holds any meaning. No experience holds any wisdom. No experience holds any concepts. No experience holds any truth. It is not that snakes are not real. Our experience of any type of snake is real, waking or dreaming. They are both equally empty. There is only experience. We single out one aspect of experience and say "this is a snake!" A snake is nothing more than an interpretation of experience. A snake is the conceptualization of only a small aspect of experience. A snake is just a concept that we use to label experience. A label is empty. Just a word or idea. A concept can be realized, but that doesn't mean there is something behind the concept.