That is an opinion within Sunniyat itself, of some scholars. Ala Hazrat mentions it in his translation Kanzul Iman in the footnotes of the translation of one of the verses of Surah Najm, and he says the other opinion is more correct [and more popular?], that he saw Allah with his blessed eyes in the state of being awake. The experience of this sight is unknown to us. it will be known to the believers in heaven, when they see Allah Subhaanahu wa Ta'aala. My understanding is that the other opinion [of seeing Gebril 'alaihis salam in his true form only, as he is the most magnificient of all angels] is due to the fact that the Prophet, Allah raise his ranks and grant him peace, has himself said that believers shall see Allah subhaanahu wa Ta'aala in the hereafter and not in this life. Our counter-explanation is that the Prophet's, on him be the choicest salutations, vision of his Creator on the Mi'raj journey wasn't in the "life of this world" per se as he had transcended this world and life as we know it, on this blessed journey, and all this is besides the fact that his blessed personality is showered by khasaais and special favors not accorded to other Prophets even, let alone common believers, so it is from his khasaais. Therefore there is no reason why this narrative should be diametrically opposite to the Prophet's stating that Haqq Subhaanahu wa Ta'aala shall be seen by the believers in the hereafter, and this becoming a case of either-or. Other than your mention of wahabis, the only people I have personally seen subscribing to this belief that the Prophet, on him be salutations, only saw Gebril 'alaihis salam in his true form and didn't see Allah - are the habashis and the other Lebanese Sunnis follow the same belief as we do. All non-shia, ie real Sunnis and claimants, believe that believers shall see their Creator Subhaanahu wa Ta'aala in the hereafter. Allah and His Messenger know best.