I'd think the hub will expand more than the spindle because it is in contact with the brake rotor. The hub could possible reach close to 200F after some very spirited braking. The spindle will likely always run cooler than the hub. This will lead to a (slight) tightening of the bearing. There is no issue on the lube film thickness. Rolling element bearings operate with microscopic film thicknesses... "elastohydrodynamic lubrication" is the term for it. This means that the film is thin enough that the asperities (microscopic high spots) on the bearings elastically deform under load, and the lube film pressure in the contact zone rises very high to provide a very slight separation of the bearing elements. The reason rolling element bearings have a finite life (as opposed to plain bearings that can theoretically last forever) is because this cyclic elastic deformation of the metal ultimately leads to fatigue and spalling of material from the surfaces. Improper tightening (tight or loose) will cause the rollers to be unevenly loaded -- more towards one end or the other, rather than the middle. The uneven loading will cause premature failure.

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1987 W201 190D