In Daniel's description of this Omaha H/L hand, he states that on the river "With the nuts straight and the naked Ace of spades, the BB raised".

My question is, what is the significance of having the naked Ace of Spades? Is it because the raise can work as a bluff, because the other person might put him on the nut flush? Or is it because he knows that the other person does not have a flush because in Omaha, it is not likely that the other person would have called the bet on the turn without the NUT flush draw? Or is it something else all together?

I'm not an Omaha player, so I don't really understand all the ins and outs of the strategy here. Any guidance would be appreciated.

It allows the person holding the naked ace to bet and put pressure on the other player in case he is playing a lower flush, as he knows he is not betting into the nuts.

Holding the naked ace of a flush draw is one of the few times a bluff will work in Omaha.