is the wheel hub bearing part of the drive axle

The drive axle, (half shaft), and wheel bearing are two different parts that are bolted together. You buy a new wheel bearing when they're noisy and making a humming sound. You do not replace the half shaft unless it was damaged in a crash. If one of the boots is split, those can be replaced separately, but that is almost impossible to do economically on some Toyota models. With no other details to go on, that's about all the information I can provide. In this case, I'd definitely believe an insurance adjuster over "someone".

You didn't say if this insurance company is involved because of a crash, or if this is an extended warranty insurance company and you want them to pay a normal repair bill.