Jaynek:
Fr. Gruner's niece became a trad due to his influence. She greatly admired and loved him. I find it unlikely that she would have arranged a funeral for him that went against his wishes. If Fr. Gruner had supported of Bp. Williamson / opposed Bp. Fellay, I would have expected the niece to know and to make the funeral arrangements accordingly.
One can argue that she did not know his wishes, so she made arrangements according to her own wishes. But you argue logically. It seems rather unlikely that she arranged for a celebrant at his funeral, whose choice, she had reason to believe, might go against his wishes.
But the thread began over an assertion by Hugh Aikins that Fr. Gruner, though silent on the matter, was fully in support of Bp. Williamson and the "resistance." I found that hard to believe when I read it the first time. I find it equally hard to believe now. Fr. Gruner's business associate, John Vennari, is certainly not a backer of Bp. Williamson. In fact, truth be told, he is virulently opposed to Bp. Williamson and the "resistance." (I use the phrase "virulently opposed" advisedly). Vennari supports Fellay & Co., and the editorial position of the CFN pretty well proves that. Fr. Gruner owned CFN. Gruner and Vennari did a weekly videoed program together, discussing a variety of topics. These two, it seems, were always on the same page with one another. I doubt that they would have gotten along as well as they did had their basic attitudes towards Bp. Williamson actually differed that markedly. But if so, then Fr. Gruner was either a pretty good actor, or able to conceal successfully from Vennari his true feelings about the bishop.