SC2Mapster

If you look at how lurker attack effect is setup you'll see that it archives the line damage by calling 10 search area (circle of 0.625 radius) effects towards the unit with 1pt spacing between each.

There are actually 2 methods to simulate & detect which units gonna get damaged.

First would involve creating dummy effect in data that would match the original search effect of lurker. Then you would need to setup a trigger that would be bound to that effect. Then in your trigger "lurker starts attacking" you would manually run that dummy effect at the position of target unit.

native void     UnitCreateEffectPoint (unit inUnit, string inEffect, point inTarget);

Second method is to do the calculations manually using circle regions. Inside an "lurker starts attacking" trigger, measure the angle between lurker and its target. Then in loop through 1 to 10 fetch units that are inside each circle going towards the angle.
Natives you will need:

// measure angle between the lurker and target
native fixed AngleBetweenPoints (point p1, point p2); 

// move the point by *distance* towards the angle
native point PointWithOffsetPolar (point p, fixed distance, fixed angle); 

// create region at calculated point
native region RegionCircle (point center, fixed radius); 

// from unitgroup fetch units that are inside given region
native unitgroup UnitGroupFilterRegion (unitgroup g, region r, int maxCount);