To a Christian cleric pagan cult objects like the Crom Cruach stone
would have been nothing more than  na bréig-dhealbha "false images".
I think that stories featuring the old deities would only have been preserved
by the monks after worship of those deities had died out.  Pagan gods
with active followers either would not be mentioned at all, or would be
mentioned only in condemnation. 
 
Charles