Is blue thread lock required when installing new rear hub assembly?

Must you, no. It's not a law. However those parts are under a lot of stress and support the weight of the vehicle. Do you really want to chance them coming loose over time because of the lack of 30 cents worth of blue Loctite? Could make for a really bad time at 60 MPH and having either one come free.

Most OE bolts use different methods of tightening, they use a preset torque tool to install them and may have locking style threads or locking inserts in the part itself. The aftermarket or replacement parts likely will not have those methods and even if you use a torque wrench it's hard to be sure things are correct. So they tell you to apply Loctite as insurance. Some OE thread locker goo is applied very thin as a coating on the bolt or threads and may not be noticeable, another trick is using different thread forms on OE parts. They look the same but are slightly different, when they are torqued into place the threads deform just enough to lock them into place.