TBF Chase cam is probably the only good excuse to not need radar as you can see your blind spots.
But for every other cam angle, radar is necessary when there is tight racing and you need to know whether you can cut tight to the apex or whether you have wheel overlap with the guy behind you and you need to take a wider line to keep from spinning yourself.
Its is also up to the lead driver to be aware of their surroundings and prevent avoidable collisions. The concept that "It's up to the guy in back of you to pass you." so therefore its ok to trust their intentions is a bit crazy to me. So many people will just force their way inside when they think they are faster than you because they just brake late. Thats what radar is good for, to know if they have enough overlap for you to adjust rather than to stay on your own line.
without radar I wouldnt be nearly as successful at clean door to door racing, but again, i use bumper cam not chase cam