While it appears the 'inside man' didn't add anything to the heist and everything that was done could have been done without him, without him the robbers would not have been aware of the facility at all. And he disabled the CCTV.
If the gold weighed 1kg per bar and there were 7000 of them (per the news story) then it weighed 7 tonnes. The carrying capacity of the van is about a quarter of that and although it's shown to be heavily laden, 7 tonnes would probably have broken it as it came out of the yard.