My Mechanic did a head gasket job on my 2000 Disco and in less than 100 miles I've got a Cracked Oil Pump. Is there a connection between the Head Gasket repair and the Pump?

 

The only physical connection between the two I can think of is the serpentine belt and that shouldn't crack the pump.

 

No, no connection.
Head gaskets fail and oil pump gears crack and break, that's just the 4.0/4.6 engine.
The timing cover(that the oil pump is inside of) is also Not removed during a head gasket job.
The mechanic did nothing to damage the oil pump.