if you ask for a snorkel to be installed, then the snorkel will be installed according to the instructions provided by the manufacturer in order to maintain warranty for you, and avoid liability issues for the dealership.
as an accessory installer at an authorised dealership that services multiple brands with 4x4 options, i have never seen an instruction sheet that requires any sealant to be applied to the snorkel seals. generally they have closed-cell foam seals at the through-panel joints, and often airboxes of off-road designed vehicles (ADR category MC - off road passenger vehicle, not class NA - utes, not class MA - suv's) have a drainage valves at the bottom, which function similarly to a heart valve - negative pressure keeps the rubber flaps together until something weighty, like water, accumulates in them, whence they open up and dump water out. generally snorkels are not designed for long-term immersion, and good luck getting a sensible and responsible dealership that wants to keep its sales rights, to make custom modifications to factory products without it costing an arm and a leg.
tl;dr - you're looking for an aftermarket product, from an aftermarket vendor.