Is there a way for an object to tell if it's being hit by a raycast?

Maybe create a bool called IsBeingHit in the respective object's script... Then use raycasts to just toggle it between true and false (By referencing the script with RaycastHit)

Note : In Update() add 2 if statements, one for when IsBeingHit is true and one for when IsBeingHit is false.

It would be better to create a function that you would use instead of raycast, which raycasts and also sends a message to any object it hits with a script. It could be like this:

 bool Raycast(Ray ray, out RaycastHit hitInfo)
 {
      bool hit = Physics.Raycast(ray, hitInfo);
 
      if (hit)
      {
           hit.collider.gameObject.SendMessage("OnRaycastHit", gameObject);
      }
 
      return hit;
 }

And on any monobehaviours you would like to know that it was hit by a raycast, you add the method: void OnRaycastHit(GameObject hitter)

@armorhide406