Yes it is OK to attach it to the road.
In the same changeset you have also attached traffic signals to the road, even though they are not actually placed in the middle of the road.

But if you do want to do attach speed cameras to the road, then you have to create an enforcement relation with the camera as device and a "to" and "from" points. 

It the camera is in the middle of the road and the camera can check both directions, then you must create two enforcement relations.

If you just tag a speed camera as a node, that is not in an enforcement relation or attached to a road, then it is useless because data consumers, i.e., navigation software cannot know which roads are monitored.