In school, I was taught to just spread some grease in the hub area between the bearings to stop rust from occurring.
Too much grease in the hub area can cause problems because if the hub is full grease, it will be churning in there and that builds heat. The excessive grease will try to leak out of the seal and can actually blow out the seal lip. This will then let contaminates in.
Here is a web site that talks about wheel bearings.
http://www.brakeandfrontend.com/whee...what-when-why/