Maybe. Depending on how his exploit works, you will need to be running emunand. It's a mute point if he gets it working on 4.5 (he's confirmed on twitter that he got it working on a 4.0 console. Here's his quote from his twitter:
So no you won't need Gateway and besides it would be redundant to try and get it working on Gateway if you happen to have a 4.5 console.
Unless you started the Gateway Exploit. His exploit appears to require a certain game (which he has not disclosed yet) to start. Thus you'd either have to use a rom of it in Gateway (no guarantee it would work like this though) or happen to have the eShop version of it installed. Since retail cartridge games can't be used while in gateway mode. You'd have to start it in classic mode to use retail carts.
It's overly complicated to try and get his exploit to work in Gateway mode. Your best bet is to just boot it in classic mode or on emunand if you want to use the eShop version of the game for the exploit. Better yet, you don't have to use the Gateway at all. Just buy the cart version of the game needed for the exploit and use that since he infer that it should work on a 4.5 console anyway.