Can non members of the church attain celestial glory from Spirit Prison?
Yes they can, and I have no doubt that quite a few will. The requirement for entrance into the Celestial Kingdom is that the individuals commit to the covenants of the Gospel of Jesus Christ. On the one hand, we absolutely claim that the LDS church is the only church with proper authority to peform these ordinances for the living and the deceased.
However, as we do perform these essential ordinances for the deceased, we do not count them as members of The Church of Jesus Christ of Latter-Day Saints. We simply count them as a brother or sister who has had their ordinance work completed, and thus submitted to them for their acceptance or rejection as spirits in the spirit world.
The reason we do not count them as members is simple. We do not know whether they will ultimately accept the ordinances peformed for them or not. Just as we had agency to choose to follow Christ or Satan in the pre-mortal life, and just as we have agency to make the same decision here in this life, as spirits after this life, those in spirit prison have agency to either accept or reject the temple work performed for them. If they accept the ordinances and have fully repented of their sins, they will be worthy of the Celestial Kingdom.