Exactly, I mean making the node a part of the way.

The hazard would still not be rendered in carto (the standard OSM rendering). But routing engines would be able to detect that a node along the way contains a hazard tag. Of course, this still requires the routing engine to look for such nodes. But at least it would be possible in principle.

If the node is off the route (as it is currently the case), the routing engine has no way to tell whether this hazard tag is relevant to the nearby path or  not; provided it even searches for nodes that are not part of the path (which most likely is not the case).