...

People interested in the overlay are able to download it from the maintained location at:

http://techpubs.spinlocksolutions.com/openldap/

Well, in that case you have to guarantee that the URL remains valid over time. If you put it in contrib/ the OpenLDAP project guarantees (sort of) it remains available. To the average potential user, I guess it's the same level of guarantee :)

It could also be listed at:

http://www.openldap.org/doc/admin24/appendix-contrib.html

as it wasn't in contrib format when I wrote this section.