It so happens that in .025 with Unrestricted Leaders, the Grigori are not allowed to research the religious techs regardless of leader. (I used Dain). It would seem this is a restriction on the civilization and not an effect of the Agnostic trait. So far, I have not had a religion spread to me so I can't say what that does. Another pecularity is that assigning an Adaptive leader to a different civilization, causes the leader to lose all other traits besides the one chosen for Adaptive.