Is the Circular Breathing a technique that is needed to know by a good Oboist?
Martin Schuring of Arizona State University music dept, and author of the book "Oboe Art and Method" writes:
Circular breathing is an essential part of oboe technique. Everyone who has learned the technique will never give it up. However, circular breathing is regarded with suspicion by some, who regard it as a virtuoso party trick that distorts the natural human qualities of music. So, it is important not to use it in that way. Circular breathing is not really intended to increase the distance between breathing points. Rather, it is a wonderful technique that can enhance playing and increase comfort. Increased comfort gives increased endurance, more stability, better tone quality, and less tension.
From that I would gather that many oboists do not learn the technique, and manage OK - but that advanced oboists find it very valuable.
A properly played oboe uses very little air and rather high pressure. It's not uncommon for quite good players not using circular breathing to play wonderfully long, lyrically sculpted legato lines audibly ending up almost suffocated. It's not as much exhaling until the lungs are empty as it is holding your breath: they end with a gasp followed by sharp inhalation.
Most non-modern music has been written without circular breathing techniques in mind, so it can certainly be pulled off without. If you are doing a competitive audition, being able to forego the gasp and wheeze might make a more sovereign impression. So the professional oboist tends to try adding circular breathing to his capabilities.