This won’t work unfortunately with the custom classes 
bool is_class(class: String) const
Returns true if the object inherits from the given class. See also get_class().
Note: This method ignores class_name declarations in the object’s script.
Surprisingly, this isn’t that easy. What I came up with is the following:
func get_type_as_string(object: Object) -> String:
if object == null:
return ""
var script: Script = object.get_script()
if script == null:
return object.get_class()
var type_as_string: String = script.get_global_name()
if type_as_string == "":
type_as_string = script.get_instance_base_type()
return type_as_string
func on_Target_hit(hit):
if get_type_as_string(hit) == target:
...
EDIT: updated the function to work with the built-in types as well
EDIT 2: update the function to work with objects without a script.