It is possible to damage the front bearing by having the differential welded?

Because the motor is damaged just after hard burnout

 

Too much tension on the front belts kills the front bearing on a rotary.

The FD has an adjuster that can fit a socket and so it is fairly common people over torque the accessory belts and wipe out the front bearing.

 

Especially if they've removed the air pump and are trying to keep the shortened belt from slipping on the water pump.