Advaita is philosophy Propagated by Adi Shankaracharya, Adi shankaracharya/Advaita(original) accepts Vedas and Vedanta Prashnatrayi(Bramha Sutras, Shrimad Bhagwad Gita,Upanishads) Scriptures while he(Adi shankaracharya so his sect) rejects all Agamas including Pancharatra which is origin of Shrimad Bhagwad Gita philosophy. Since there are some Shaiva and Shakta Agamas which have Vamachara followers, so does Advaita Sect accpets them as these(vamachara) people claim to follow advaita philosophy. If Yes, then how is it justified to include agama followers in a sect which rejects all agamas?.
In his book The Spiritual Heritage of India, Swami Prabhavananda says (pp 143-145, section heading: The Tantras):
The Tantras are the scriptures by means of which knowledge is spread in order to save humanity from ignorance. They are also known as Agamas--revelations, in conformity, that is, with the revelations of the Vedas. Their authorship is unknown though there is a tradition that Siva uttered them to his divine consort Sakti (the Divine Mother), and that through her they reached mankind. Their date is uncertain, but since Buddha was familiar with them they are obviously pre-Buddhistic. Buddhistic Tantras exist, however, belonging to the Tibetian school of Buddhism.
The original Tantras are divided into three main groups according as the deity chosen to worship is Vishnu, Siva, or Sakti. Thus there are Vaisnava Agamas (or Pancaratra), the Saiva Agamas, and the Sakta Agamas, besides the later Buddhistic Agamas composed in Tibet. The Sakta group is the most popular, so much so that the word Tantra has come to mean, generally though mistakenly, only the Sakta Agamas. It is those that we shall give our attention.
The Tantras are broadly divided into three parts; sadhana, which include spiritual practices and disciplines and ritualistic forms of worship; siddhi, or attainments from such practices; and philosophy. Let us examine the last of these first.
The philosophy of the Tantras is based upon the Upanishads. It is nondualistic,, upholding the identity of the individual soul with Siva-Sakti--that is, in the language of the Upanishads and of Samkara [Adi Sankara], the identity of the individual self with Brahman, ot the Universal Self. Samkara calls the creative power of the universe maya, or illusion, the universe for him possessing in itself no absolute reality, whereas the Tantras call the creative Sakti, or God the Mother, and regard the universe as her play when she has become mind and matter. Here, in their interpretation of reality, the Tantras apparently approach the philosophy of Ramanuja, who looked upon the universe of mind and matter as a transformation of Brahman--as, in effect, the body of God.
This Sakti, or God the Mother, is not distinct from Siva, or Brahman, the Absolute of the Upanishads, but is the power of the Absolute. In the transcendental plane, which is static, where there is but one undivided, absolute existence, and where there is no universe, the truth is known as Siva, or the Absolute Existence-Knowledge-Bliss; but in the active, immanent plane, that is, the plane in which the universe is known, there is experienced by the seer the play of Sakti, of God the Mother.
...The teachings of the Tantras are never at variance with those of the Upanishads.
In his footnote to the first sentence above, Swami Prabhavananda says:
Of all Indian scriptures, the Tantras are most often misunderstood by Western scholars, and even native scholars are not altogether free from error in dealing with them. But I must declare in this connection that in recent years one Western student of Eastern philosophy, Sir John Woodruffe, an Englishman and at one time Chief Justice of the High Court of Calcutta, has through a lifetime devoted to the study of Tantric literature, done yeoman service in the cause of a proper understanding of these difficult scriptures, both through translations of original manuscripts and through correct interpretations of their spirit. 'Tantra Shastra [scriptures]', he says, '--(is) generally spoken of as a jumble of "black magic", and "erotic mysticism", cemented together by a ritual which is "meaningless mummery". A large number of persons who talk in this strain have never had a Tantra in their hands, and such Orientals as have read some portions of these scriptures have not generally understood them, otherwise they would not have found them so "meaningless". They may be bad or they may be good, but they have a meaning. Men are not such fools as to believe in what is meaningless.'
Vamachara has been universally condemned by all seers as a path as the vast majority of people that try it easily fall further into tamas and materiality. What is thought of as Vamachara practices make up a very very small part of the Agamas, and is most often misinterpreted in wrong ways when it comes to the practice. Swami Vivekananda condemned the practice of Vamachara. Although Ramakrishna Paramahamsa would not condemn anyone and only referred to Vamachara as the sweepers back door entrance to a house, he did not condone it or accept it. He looked down on the practice and always encouraged the correct path and would have nothing to do with those who practiced it.
As a final note, most people do not realize it, but the pujas that are celebrated by everyone are based on the Tantras.