If you could post the exact model or pictures of the Dynohub perhaps someone here will be able to provide more information about it.

Either way, if it is a 6 volt/3 watt dynamo it should be compatible with modern lights.

edit: according to Sheldon's site, an old SA dynohub might be 1.8 watts. Probably depends on the exact model.

Shimano currently has a modern dynamo hub, the DH-1N70 which is a 1.5 watt model so there are ostensibly modern lights that will work with this lower wattage. I don't know how much light one could get out of this lower output though.