A little of both. When you've got a decent set of aces like this, you should certainly be 4-betting preflop. In a 4-bet pot, you can usually get SPR's that are conducive to stacking an overpair in Omaha if you're 100 bb's deep.
However, this is sort of a special case. Our opponent has 300+ bb's, so normally we shouldn't be looking to stack off with just an overpair in a 4-bet pot, since there's so much more money behind. But against a true drooler, I say just get it in, since this board is dry enough.
Omaha's a little funny though in that you're not really looking to push your preflop edges (since they're small). Get position with a good hand, and then pound him mercilessly when you hit flops (and if you're selecting good hands, you'll hit more flops & hit them harder). Players like this almost always push their hands too far postflop, so they offer good implied odds
even though they start out with bad hands.