Sorry for my late response here.
In section 3.1 the 2017 rules state:
The robot must not emit infrared light. However, optical sensors (e.g. infrared-distance-sensors) may be used as long
as they do not affect other robots. This needs to be proved by a referee or an OC member if a claim is placed by the
To reiterate, your point of view was indeed correct: the only problem (from the rules' point of view) is the situation when both teams use them and interference of some sort occurs. If that does not happen, they can be used in Open without any issues.
Hope this helps,