Of course e can be evidence even if P(X|e)=P(X) -- it just cannot be evidence for X. It can be evidence for Y if P(Y|e)>P(Y), and this is exactly the case you describe. If Y is “there is a monument and left is red or there is no monument and left is black”, then e is (infinite, if Omega is truthful with probability 1) evidence for Y, even though it is 0 evidence for X.
Similarly, you watching your shoelace untied is zero evidence for my shoelaces...
Of course e can be evidence even if P(X|e)=P(X) -- it just cannot be evidence for X. It can be evidence for Y if P(Y|e)>P(Y), and this is exactly the case you describe. If Y is “there is a monument and left is red or there is no monument and left is black”, then e is (infinite, if Omega is truthful with probability 1) evidence for Y, even though it is 0 evidence for X.
Similarly, you watching your shoelace untied is zero evidence for my shoelaces...