Physics.Raycast will raycast against every object within the layers specified by the cullingMask which you leave as kDefaultRaycastLayers, not just against just your player as your question states that you are expecting.

• hit is a RaycastHit, not a GameObject. hit == GameObject.FindWithTag("Player") will always return false. You should probably use hit.collider.gameObject == GameObject.FindWithTag("Player") which will actually work.
• You declare the InSight variable within the scope of the two if statements and then try to access it in a different scope. This will not work.
• Why do you even bother with GameObject.FindWithTag("Player") within your raycast if when you store the transform of this GameObject in target?
• You check a boolean condition to set hunt, but you only use it in one place. Why not just check the condition itself? Isn't it the same with inSight?
• You calculate target.position - transform.position up to five times - why?
• You do essentially the same thing in all three if statements. Why?
• You're not supposed to pass Slerp/Lerp a deltaTime, but an incremental time value unless you want it to always look some small amount towards the target. Since you are also slerp/lerping from a constantly changing rotation to a potentially constantly changing rotation by some tiny control amount, you will never actually reach the target unless your frame rate should slow significantly (in your case to rotationSpeed frames per second).

This does what it seems you are trying to do and should actually accomplish it (Note that the Slerp here is not framerate dependent anymore):

var target : Transform;
var huntRange : float = 20.0f;
var rotationSpeed : float = 0.1f;
var moveSpeed : float = 3.0f;
var runSpeed : float = 5.0f;
private var speed : float;

function Start() {
    target = GameObject.FindWithTag("Player").transform; 
}

function Update() {
    var hit : RaycastHit;
    var direction : Vector3 = target.position - transform.position;

    if(direction.magnitude < huntRange
        && (Physics.Raycast(transform.position , direction, hit)
            && hit.collider.gameObject == target.gameObject)) {

        //Shorter than writing 2-3 ifs that do the same thing
        if(Player_Simply.running) speed = runSpeed;
        else speed = moveSpeed;

        transform.rotation = Quaternion.Slerp(transform.rotation,
                                    Quaternion.LookRotation(direction),
                                    rotationSpeed);
        transform.position += transform.forward * speed * Time.deltaTime;
    }
}