You mean like blessing their endeavors through the Litanies of their Chaplain? There are no atheists in foxholes, and The Emperor Protects.
the entire point of the "no atheists in fox holes" argument doesn't apply here. the argument is that in the hard enviroment of combat, where simple bad luck could see you dead, or worse, even people whom have abandoned their religion will find themselves praying. the argument falls apart regarding space marines on two accounts.
1: Space Marines are raised in a chapter cult that useally teaches that the emperor is NOT a god, but simply the greatest human.
2: Know no fear. Space Marines are conditioned to be pretty much immune to the kind of tension being discussed. as such a Space Marine in a fox hole is only going to be thinking "Ok, I should proably get out of this fox hole"
doesn't address that the line is wrong anyway.
the thing is Marines know what a psyker is, and know the emperor was the greatest psyker. thus they're less prone to describe things as miracles then the less educated normal humans.