Actually, I am pretty sure the "port" on the hub is an OIL port.

Garden variety bike grease is just oil and soap. The oil provides the lubrication, the soap makes it stay around. Soap, though, can absorb water, which can cause problems in bearings. Waterproof greases are different. In either case, grease takes force to flow very far and get pushed into small spaces, like between ball bearings.

Years ago (well, 30 years ago, when I got out of the Army and into bike riding and probably way before that) Campy was making it's racing hubs with oil holes -- p[robably long before that, too.

You have to oil more frequently (like weekly), more often if rainy, compared to rebuilding the hub with grease, but oil will flush out the bearings so you should be able to go longer between rebuilds, if you re-oil frequently. If you wanted, you could ignore the oil hole and grease them as with any hub without an oil hole.

Trying to force grease into the hole in the hub would not accomplish much unless it has a "zeek" fitting where you would use a grease gun to force grease into the hub and _through_ the bearings under pressure. Otherwise, the grease really won't go anywhere except into the voids around the axle.

So, you can grease the bearings, as most people with rebuildable bearings do, or clean them out and convert to oiling them every few days through the hole.

A couple people I knew in my early cycling days would convert their non-Campy hubs to use oil bu drilling an appropriate hole and buying a Campy (or other?) spring clip that would go around the hub and plug the oil hole against contamination.