You can selectively group the edges that need to be dashed and assign a dashed layer to that group, not to the edges. The edges will inherit the layer’s dash behavior from their group, the same as they inherit layer visibility. This technique also avoids questions about why some of the edges in a group are dashed but others are not and why dashed edges break non-dashed edges.
Edit: rules are made to be broken. If you are expert and fully understand the implications, nothing in SketchUp prevents you from doing dangerous things with layers. But others are best off following the guidance.