Yes, in all the proceedings, the only things alleged of Father Fullerton were --
1) one second-hand statement that he had no problem with the boys skinnydipping at some camp run by Urrutigoity.
and
2) "cussing out" someone who had certain accusations against Father Urrutigoity
With everything going on, I'm guessing it would have come out if he had been an actual participant in such activity. Urrutigoity was well known for snookering and manipulating people. He could have had him fooled, much like he fooled Bishop Williamson, into thinking that the poor guy was just being unjustly persecuted. Until something comes out, only God knows.
Interesting story. Just before Father Urrutigoity's last year at seminary, I left STAS to become a sedevacantist. Bishop Williamson had me corresponding with Father Urrutigoity, as the latter sought to win me back. Father U had sought to induct me into his click, but I didn't want to have anything to do with them. He took an interest in winning me back after I left. So we exchanged some theological letters. I went to his ordination the following June, and he told me that he had offered his first Mass for me. Later someone told me that he told him the same thing, that he had offered his first Mass for someone else. He knew what to say to try winning people over.
Father U was a liturgical experimenter. He tried to introduce "troped" Kyries into the Mass ... even though these had been banned after the Council of Trent. At one point he wanted women in the seminary choir area to sing. I objected to the powers that be, and Father U was overruled. I don't think he liked my interference.