In this chapter of the Vaishnava section of Skanda Purana, Vaishnavism is described in great detail. The Advaitic identity with the Supreme Lord is mentioned in this chapter on the Vaishnavites who apply markings of chakra, etc. on their body.
स्कन्दपुराणम्/खण्डः २ (वैष्णवखण्डः)/पुरुषोत्तमजगन्नाथमाहात्म्यम्/अध्यायः १०
पश्यताश्रमवर्णोक्तान्धर्मान्नैव जिहासता ।। ८५ ।।
आत्मज्ञानाय या भक्तिः क्रियते सा तु सात्त्विकी ।।
जगच्चेदं जगन्नाथो नान्यं चापि च कारणम् ।। ८६ ।।
अहं च न ततो भिन्नो मत्तोसौ न पृथक्स्थितः ।।
This world is verily God. Brahman is the material cause for this world. Only then can the world be called Brahman. Also, 'I am not different from that Supreme Lord'.
This statement conveys the deminal premise of Vedanta: Brahma Satyam Jaganmithya Jivo Brahmaiva Naaparah (Brahman is the Only Reality, the world is unreal and the individual soul is verily Brahman). Scholars recognize that it is a case of Baadhaayaam Saamaanaadhikaranyam (बाधायां सामानाधिकरण्यम्) because the world is called Brahman without directly saying that the world is illusory.
And Jiva Brahma abheda is quite explicit in the above verse.
रथचरणगदाब्जशंखमुद्राकृतितिलकांकितबाहुमूलमध्याः ।।
मुररिपुचरणप्रणामधूलीधृतकवचाः खलु वैष्णवा जयंति ।। १५ ।।
The above verse says that the Vaishnavas don the chakra, etc. marks on their body by branding, prostrate to Vishnu, etc.
हीनं बहिरुपाधीनां प्रेमोत्कर्षेण भावनम् ।। ८७ ।।
दुर्लभा भक्तिरैषा हि मुक्तयेऽद्वैतसंज्ञिता ।।
This devotion leads to advaita mukti.
सात्त्विक्या ब्रह्मणः स्थानं राजस्या शक्रलोकताम् ।। ८८ ।।
प्रयांति भुक्त्वा भोगान्हि तामस्या पितृलोकताम् ।।
पुनरागत्य भूर्लोकं भक्तिं तां वैपरीत्यतः ।। ८९ ।।
तामसो राजसीं कुर्याद्राजसः सात्त्विकीं तथा ।।
सात्त्विको मुक्तिमाप्नोति कृत्वा चाद्वैतभावनाम् ।। 2.2.10.९० ।।
They are sattvikas, the muki they attain is advaitic in nature.
Are these Vaishnavas demons, of illegitimate birth?
Following the interpretation of the 16th chapter of Sri Raghavendra Tirtha's GitaVivriti, in the book 'Manimanjari Vaibhava', the Advaita doctrine which says that the world is illusory, is demoniacal, and asserts that the Advaitins are Asuras and that they are all born illegitimately. In this book, 'Avaishnavatva', practicing 'Bhasma, Rudraksha' ritual is also mentioned as a reason for their being demoniacal in nature.
According to the above 'Nyaya', dictum, now these Advaitin Vaishnavas of the Skanda Purana are demons and born of illicit relations.
Even Vedavyasa who advocated this Chakrankita Vaishnava Advaita in this chapter and Advaita without the Chakrakita epithet in Bhagavata, Vishnupurana, Skanda, Padma, Vayu, Varaha, Brahmanda, Garuda, Shiva, etc. puranas, partakes of this Gita vivruti (of Raghavendra Tirtha) dictum (as explained by the author of the book: manimanjari vaibhava) of demoniacal nature and tainted birth.