Have seen a few not with that specific advice but conspicuously "sticky" sealant banding. I'd be surprised if the Hylomar diminished any included sealant's effect on a gasket. Besides, as a contrarian, the first thought I'd have on reading a notice like that would be: "Oh yeah? Just watch me." Although, it would be trialled on my own vehicles.
Shellac based sealers would be another story; easy to imagine them blunting the effect of a modern product. A bit like trying to paint on a chalky surface. I've seen too many marginal situations - poor liner protrusion mainly - saved by the use of Hylomar, to be comfy without it.
Given our OP's location, he's going to get raped on gasket spray more than Aussies do, if he does go that route. That'd suck.
Likely you're right, but I'm one of those who normally likes to follow the manufacturers instructions to the letter, and then if there's a problem you can grab 'em by the throat.
I used to spread red Hermetite around like jam when I first started playing with engines, but modern gasket sealants are much better and less messy. Trouble is, it's a lotta work replacing a head gasket, and a real pain in the @rse having to strip it again if summat ain't right....
'56 Multispace 1.6HDi - Iron Grey