Is a dream object an existent? How about the face in the mirror?

The context for this question is contemporary Tibetan Buddhist Monastic debate and associated definitions as practiced at Sera Je Monastic University. I'm looking for answers according to the specific definitions and system of jargon used in that context. In Tibetan Buddhist monastic debate according to The Course in Buddhist Reasoning and Debate an *existent* is defined as, "that which is realized by a valid cognizer." I'm asking whether under such a definition a dream object - such as a snake - is considered an existent or a non-existent such as the son of a barren woman. I believe that it must be considered an *existent* as it is known by a directly perceiving mental consciousness given the above context. 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 from viewpoint of above context? Is it true from the Prasangika viewpoint? I posit that a dream snake and a snake I perceive in waking life are both conventionally existent. Further, that neither are ultimately existent. And that neither are real except from the perspective of a worldly consciousness. That is, they are both equally unreal. Is this true from the Prasangika viewpoint? If not, please give reasons according to the context mentioned above.