In my very personal opinion we must adopt some portions of the Dasam Granth Bani which suits KHALSA PANTH AND IDEOLOGY OF SRI GURU GRANTH SAHIB even if we prove that it is not the Bani of Dasam Guru Sahib. Yes I may be 100% wrong. Sadh Sangat bakhshanhar hai.
The question is not to 'adopt' some other scriptures (or parts of 'em), the question is, Do we 'consider' Guru Granth Sahib Ji as our only Guru or not? Guru Gobind Singh Sahib presented the 'Gurgaddi' only to the Sri Guru Granth Sahib, and coronated the 'word' as the Guru. That was the 'most' important event in the life of Sikh faith, we find no parallels elsewhere in the world. But, since the 'Brahminists' could not digest the 'Charhdikalah' of the Panth, they planted the Dasam(?) Granth to parallel (but in vain) the glory of our beloved scripture, to separate us from our Guru Sahib. We should not tolerate this nonsense anymore. Tons of evidences are against the Dasam(?) Granth. Adopting protions of the DG would only bring bad tidings for he Panth and dilute our 'Tatva-Gurmat' philosophy.
I personally 'like' many novels and poetry books, some of them are even spirituality based, but does that mean that we give them respect equal to our scripture. All the rest may be good, even perfect, if you may say; But, only the Guru Granth Sahib is our Guru, who are we to challenge the Tenth Master, Guru Gobind Singh Sahib who himself had appointed Guru Granth Sahib as the 'Guru' in front of the whole Panth??