Unreachable points are points that don't reach an output pin and therefore don't affect a primary output logically. It appears the diodes don't matter in the functional compare of your design and can be ignored.
I presume the design has no non-equivalents related to diodes.
That is probably the best way do the compare. One option is to write out a netlist without them. Another option is to use the LEC remove command but that has a certain danger to it.