I agree with HNeedham wholeheartedly. For smaller services, it can often be much more cost-effective - and just as good (or even better) for users - to share existing cataloguing infrastructure.

I know of a small local studies library in the States that pays a nearby university a small rent to share the university's library catalogue and that works very well for all concerned.

I agree with Heather that the standard should definitely not be so prescriptive here, and I speak as an archivist in a service that has its own stand-alone online catalogue. Contributing to aggregated catalogues should have the same weight as a stand-alone catalogue.

I also agree with AJanes that archival institutions fortunate enough to have the funding the provide an in-house online catalogue should be encouraged to offer a "renting" solution to smaller organisations. Whether on a thematic basis or a geographic basis there are real benefits to users as well as the smaller organisations.