I understand that dark matter only has a gravitational property. It does not interact directly with regular matter or EM radiation. The evidence for dark matter comes from observations that contradict known gravitational law. (Rotational velocity of galaxies that are far away is constant regardless of distance from galactic center). This and other data has indicated that dark matter only interacts through gravity.
Since gravitational lensing of light near black holes has been demonstrated, it is expected that large gravitational distortions from dark matter can also distort light. Has this been seen?
Can the increasing redshift of light with distance be explained by the cumulative of effect dark matter exerting a gravitational force that is directed away from us?
Another way to think about this is to consider that our observable universe has a fixed dimension. There has not been enough time for light to reach us from stars beyond that dimension. However, if the actual universe were much larger than the observable universe, and it was all filled with dark matter, would we not see its gravitational effect on light that was emitted from the boundary that we can see? (as long as the dark matter was not homogeneous) This following explanation suggests that dark matter homogeneously distributed in the cosmos can not have gravitational effects. http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshell2.html
Basically, the force from any spherically symmetric mass distribution on a mass inside its radius is zero.
So that means that dark matter is not homogeneous in the universe. The density of dark matter has been calculated as well.