I agree that an excessively tensioned drive belt will not help with bevel box noise but the main reason for the noise is the running clearances on the BB gears, particularly when up to running temperature. Quite how much bearing the various possible causes for the variations in clearances have on this seems to be a mystery, with several knowledgeable people and companies trying unsuccessfully to come up with a definitive fix for this problem. I really don't think that a tweak of the belt tension and tracking of the belt and rear wheel is the real answer, although these may all improve things a little.
If someone can come up with a 100% guaranteed fix for a noisy bevel box, then I may be tempted to pay some money for a quiet BB. No one has said they have sorted the problem 100% for sure yet, some claim improvements but not "a fix".
The prop shaft runs pretty straight and therefore the UJ bearings hardly move, brinelling being a consequent problem rather than a problem with out of alignment.
