If you look at the recipe link, it says 1/2 cup of sugar and 1/2 cup of hot water, which won't be a lot in a 13 x 9 pan, which is why it says to drizzle the water on.

That's also the same ratio as the standard formula for making simple syrup.

This batter is really thick, you spoon it on and spread it around with a spatula. With a thinner batter, the sugar might start to dissolve into the cake batter. It might still work, but maybe not be as definitive a layer. Waiting until part way through the baking process might work better but be more challenging to do since you're working with a hot pan at that point.

Might be worth some experimenting.

The technique in a Texas Chocolate Sheet Cake of pouring a warm frosting onto a hot cake is not very commonly used, most recipes have you wait until a cake is totally cool before frosting it, in large part because the heat would melt the fat in the frosting. It tends to compress the cake slightly, which is what makes it a bit more brownie-like in texture, I assume, and it holds in the moisture that would normally escape as the cake cools.

Would this work on the top crust on a pie?