All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu`alayhi wa sallam, is His slave and Messenger.
There is no harm - Allah willing – upon the Muslim if he attends such a conference to get benefit from the knowledge of the Sunni scholars who would attend it. Organizing this conference by some people of Bid'ah should not serve as a reason for preventing the Muslims from attending it for benefit. In addition, wisdom is the lost property of the believer, so wherever he finds it, he has more right to it.
As for the participation of those Sunni scholars with those innovators in a matter of good, it is lawful, since the Muslim cooperates with all people to realize the Sharee'ah's interest. Allah, the Exalted, says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty.} [Quran, 5:2] Besides, it is narrated in the Hadith that the Prophet said, “I have witnessed an alliance in the house of ʿAbdullah ibn Jadʿaan. It is better to me than hundreds of camels. Even now in the period of Islam, I would respond positively to attending such a meeting if I were invited.” [Al-Bayhaqi] It is known that this alliance had been established on the rule of supporting the wronged.
Allah knows best.