Sure, you can make your purchase from your own AcousticSamples account then you will receive by email a serial number that you can offer to someone.
The lucky person you give the serial to can simply create their own AcousticSamples account in order to register the serial number.
Detailed instructions on how to register, install and activate AcousticSamples libraries can be found on this page: https://www.acousticsamples.net/faq