Currently IOR can only create passthrough TLS Routes, it is hardcoded.
OpenShift Routes can have two other kind of TLS termination: reencrypt and edge.

It should be possible to use Istio with re-encrypted or edge terminated Routes (most common use cases I've seen).

I don't know if it's already doable today based on Gateway TLSmode, if upstream Istio needs to be extended for IOR to parse such settings or simply adding an openshift label on the Gateway resource to inform the IOR process how to handle the TLS termination in an OpenShift Route specific way.