Only with copious amounts of solvent using strong turbulent flow and flushing for a long time.
I don't think you'd be able to properly and completely wash out the factory grease on a practical level.
I have trouble cleaning them even when they're all apart, especially the seal grooves.
Well... it'll have to do, because this particular unit is a Hub, and it's not even supposed to be user servicable. It goes bad, it goes in the trash, and then you have to hunt down another, and pay through the nose if you can find it.
Better than nothing I suppose.
No, it's not better than nothing. You'll mix solvent with the remaining grease that you won't be able to get out. Once you pack in the new grease, the solvent will change the lubrication properties of the grease, making it worse than before.
Manufacturers use rather good grease in their bearings. The original grease charge can easily last a long time (the life of the vehicle), as long as the seals keep the water and contaminants out, and the grease in.
It's not the grease you should be worried about, it's the seals.