You don't need to check registration. In the Apple world registering software really doesn't have much of a purpose.
If the software was bought on DVD and you have the serial number you are free to give it or sell it to anyone you wish. Just keep in mind that Aperture 2 is very old and while it (sort of) works on the newer OS's it really isn;t a good solution for anyone serious about using Aperture.
It would be OK for someone with older hardware that is unable to upgrade past Snow Leopard but for anyone with newer hardware it would be a mistake to use.