If that's a license question, do whatever the License says I guess. You could do both just to be safe.  If that's a question to the hosts we don't mind. 

Every sound there has a different license. CC0 ones do not require that. You can basically click on the license in the interface, afaik.

It's always better to just give the credit irrespective of the license! If we devs picked something we liked then the least we can do is promote their page! I always love to credit!

:)