They previously used grease when other companies were Oil Bath. The company was more pleased with previous grease hubs successes over time. They felt the only reason grease hubs gave issues were related to usage of a grease gun on the end bearing caps, pressurizing and blowing a two way seal. With Vault there is no lubricant remaining in a seal failure.
Vault hubs were endorsed by the previous UFP ownership and the success was acceptable in prior years. Lately there seem to be more issues right on the five year time line. The grease hubs also require nothing special, other than parts, to service and the thixotropic grease is harder to find.
The reason for DOT 5 is reducing rust in older brake systems as DOT 5 is not hydroscopic and doesn’t absorb moisture. It is also a thicker fluid.