Yes, a bad bearing can cause a leak and yes a leaky seal can also wash out the grease in the bearing since the oil has to leak through the bearing to get to and past the outer seal.

If/when you get an oil leak, I'd recommend using a needle attachement on your grease gun, sliding it under the bearing seal lip and filling the bearing back up with grease when you replace the seal. Might be a good idea any time you have your shafts out for that matter (while swapping a 3rd, etc.).

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik