I have one of the eBay silicone hose kits.
3 layers, just like the silicone couplers that I have for my IC piping, and the upper radiator hardpipe. Inner layer of silicone, middle layer of braided nylon fibers, and an outer layer of silicone. Specific density of the silicone matches that of Vibrant branded parts, making me think that it's a very similar compound. Should be proof against casual oil contact oil or coolant. The only line that I know of in that kit which is in contact with oil is the breather line between the head and block, which shouldn't be flowing oil, but may come in contact with it. I don't think that the stock line would survive flowing oil for long either given how brittle it has become over time. I believe that I can expect reasonable service life for the coolant lines included in the kits.
I'd be fine with stock, but stock is more expensive. I believe that expense is the reason why the stock lines aren't silicone. It is more expensive to produce, therefore is a poorer choice for OEM.