well it will "work" but how much flow you end up with will depend on a few things.
which system is higher than the other, the display or the sump? If your display is higher then you can still use gravity for your drain from the main and use your pump to return. This is a typical set up.
How much flow you'll get will depend on how "straight" your return plumbing is going back to the display. Even though it's only 18 inches in verticle rise, each bend and coupling in the plumbing will add resistance and slow your flow some.
You might consider using a larger diameter pvc
for your return to help reduce the back preasure caused by the turbulance at joints and elbows. Also, if things turn out to be too slow, you could go for a larger return pump and already have the larger pvc
plumbing to handle it.