VP actually do recommend the use of their or OMC gasket sealer/ cement on the driveshaft bellows ( but not on the exhaust bellows). The same stuff that's recommended for the water inlet O ring fitted to the pivot housing..

For the DPS/ SX transom assembly it's applied on the transom shield stub and inside of that end of the bellows, plus on the tilt housing and the inside of the lip on tilt housing end of the bellows; where the bellows pulls through the pivot housing.
For the SX/ DPS fitting the outdrive ( with waterproof grease on the "nose" of the bearing/ seal housing) forces together the tilt housing and outdrive to the bellows.

Earlier drives had a hose clamp on both ends of their drive shaft bellows, rather than the single one at the transom end on the SX/ DPS

I didn't notice any suggestion for it when I replaced mine last year. No leaks. But, I suppose it can't hurt, as long as it doesn't make it too difficult to get off.

I'd always used gasket sealant as per the factory manual on my previous boat; never had any water ingress in the 5 (6 month immersion) seasons I used it.

When I took the original bellows off by 2004 boat after 6 months iin water there was evidence of slight water ingress ( small ammount of salt water in there and very light rusting on the driveshaft yokes; I reckon I caught it just in time)). There was no sealant on the bellows from the factory ! To me, that was enough proof that the gasket sealant makes the installation more secure/ watertight.

Guess what? I always used the sealant since and have never had any more water ingress !