From how you describe it (I've never come across the term but I'm by no means an expert), Hydraulic lock sounds like what would happen to any actuator if it failed (ie hydraulic fluid in both chambers.)
Jack stall occurs when the actuators are still working but they can't apply enough force to overcome the aerodynamic forces. So they 'lock' momentarily.
So, 'is there a difference?' Yes. One is a permanent failure of a component. And the other is a temporary exceedance of a design limitation (to put it kindly.)