If you complete the raid on Hard mode you get the Radiant rewards from Normal mode as well but not the other way around. The only rewards you can't get on Hard mode are the Special and Heavy weapons meaning that if you are missing the the shotgun, fusion rifle, sniper rifle, heavy machine gun or rocket launcher you will have to play on Normal mode and hope to score them there. Hard mode only awards primary weapons like the hand cannon, pulse rifle, scout rifle and the auto rifle. Normal mode awards character class items, "Cryptographic" shader, "Light In The Abyss" Legendary ship and "Crota's End" Legendary Emblem. Hard mode rewards players with "Bane of Dark Gods" Legendary ship, S-13 "Graverobber" Legendary sparrow, "Glowhoo" Legendary shader and the Crux of Crota Exotic item used to upgrade Eidolon Ally into the Exotic primary rifle the "Necrochasm". Also, you can only reap the rewards of the two chests and the Death Singer once, meaning that if you opened both chests or killed the Death Singer on Normal mode on Hard mode you will get nothing respectively.