u can reach the water pump by putting our hand down the back, make sure engine is cold
no they shouldn't use sealant as they are metal gaskets nowadays rather than the old cork ones
the metal ones allow for a much better compression seal and can handle heat expansion from both head and block
if your hg is leaking then either he did not get the head skimmed, pressure tested, did not clean it properly or failed to replace seals an bolts
I seen complete c*nts use sealant on engines when they couldn't be arsed to replace seals, its like resealing your bath with silicone lol