OK, so you can confirm that there are rubber seals, aka wiper seals, on that hub. These seals don't work the way most people think and like others here suggested, a little seepage is to be expected. Seals cannot prevent that and should not prevent that.
A rubber seal is a contact seal. You can visualize the seal as a rubber blade with a thin, feathered edge, that runs on top of either the outside or inside radius of the two parts rotating against each other. Usually it is fixed to the larger radius and wipes on the smaller radius, where the speed is slower.
If you rub a standard pencil eraser over a smooth surface or indeed, paper, you'll notice a streak of rubber behind the rubbing line. This is the rubber being torn off the eraser by friction between the rubber and the paper. Should the same happen when the wiper seal runs on the metal, it will quickly burn away. Just a few revolutions of the wheel and the seal would have abraded sufficiently to no longer make contact and consequently, it will remain at that diameter forever. If it doesn't make contact, it cannot wear out.
However, they tend not to wear out this quickly and this is not something to do with the type of rubber but the design of the wiper seal. It is designed to allow some grease to escape under the lip and work its way outwards. This escapee grease lubricates the seal as it slides over the metal and keeps it intact for many thousands, even millions, of revolutions of the wheel. However, escaping grease cannot last forever. Eventually the bearing loses so much grease that it can no longer feed the seal and that's when seal damage occurs. That's why grease should periodically be repacked.
A second issue is that now that we've stated that the seal doesn't really seal (it allows grease to migrate), we have to realize it will also allow water to migrate inwards. In engineering there's an adage that says a single seal cannot successfully separate two liquids (in this case, water and grease). Therefore that wiper seal has to be protected by a secondary seal, the so-called dust cap or labyrinth seal. That's the metal ring you see just outboard of the rubber seal. That's a non-contact seal that prevents water from splashing onto the rubber seal which cannot separate water and grease. This way the rubber seal doesn't receive a direct hit of water and it can do it's job of keeping the grease in, and clean.
During a bearing's life - we're talking unopenable cartridge bearings here - it will always seep grease. The minute the grease stops seeping out, the bearing will start deteriorating quickly. Not because it is now worn, but because the grease is now depleted. It is common to open machines or even bicycle wheels and see a ring of grease just outside the seal. That grease used to be inside the bearing and migrated out, doing its job of lubricating the seal.
To make a long story short, repack your bearings for time to time and expect to see some grease coming out.
