No, the melon organ will be way less useful on land, due to the impedance mismatch.
Before you report me for insulting, let me explain what is it ;)
When an acoustic wave travels from a medium A (let's say water) to a medium B (let's say oil), the amount of transmitted and reflected power at the interface depends on a property called acoustic impedance, which you can see somehow equivalent to the electric resistance.
The maximum transmission of power from A to B, and conversely the minimum reflection, happens when the acoustic impedance of A matches the acoustic impedance of B.
If the impedance mismatch is too high, you end up reflecting most of the power back, instead of actually transmitting it. This is why when you get an echo scan you get smeared with that gel: to remove the layer of air between the transducer and your body, increasing the amount of ultrasound that goes into your body for the scan. And this is also why underwater explosions are way more destructive on a human body, for the same amount of explosive, than in air explosions.
Coming back to the melon, it works well underwater because its impedance matches well with the water. If you use it in air, you will have a poor matching, unless you spread gel from the melon to the target of the scan.
Bats solve the issue by using their vocal system and auditory system directly in air.