yes we can see something on TCAS
Its that the training deptments are trying to stamp out.
The call to say visual is completely diferent because it is calling a statement of fact and you can presume that they are going to see and avoid.
For example if you declare visual with traffic a procedural controller can the give you a visual climb/decent against with both aircraft being happy. They couldn't if both planes have each other on TCAS.
Having something on TCAS means nothing at all. And can lead the ill informed presumption that they are seperated when they arn't. In a radar enviroment it just takes up air time for zero safety increase. Even if you do have something on TCAS you don't alter anything to try and avoid that contact until it gives you a resolution. Mode A only squawks are a complete pain to deal with because you will only get a traffic advisory on them even if you are sitting happy at FL180 in controlled airspace.