LS/Vtec combinations are just as reliable as a all OEM engine, what it comes down to is how the engine is built and how you the driver drives it. THE main complaint i get about LS/Vtecs are that the rod bolts break and there are alot of oil leaks.
the answer to this is to upgrade your rod bolts OR use forged rods/pistons, and the oil leak part is due in part to how it was assembled. if your going to run the piss out of the engine then either one will fail in the end no matter what, its inevitable.