Turning up and putting in a good performance of any song is an adequate tribute to Glenn. A tribute show is still predominantly, a show, not a ceremony. The people who except the invitation or volunteer to perform should not have to face a strict vetting procedure.
I think I'm the only person who felt that
Let It Be was a highly inappropriate choice of song, for Paul McCartney to perform at the mid eighties, high profile, televised, Live Aid Concert, to raise money and awareness for the starving victims of an African Famine (not forgetting Bob Dylan's, "odd million for the poor american farmers"
) but McCartney's performance was a highlight.