import bpy
import inspect

#https://blender.stackexchange.com/questions/90535/selecting-all-objects-that-have-been-specified-in-modifiers

def select_objects_in_modifiers(obj):
    rna = obj.bl_rna

    refs = set()
    for mod in obj.modifiers:
        for key,val in inspect.getmembers(mod):
            if val is None:
                continue
            if hasattr(val, "bl_rna") and val.bl_rna == rna:
                refs.add(val)

    for o2 in refs:
        o2.select = True
        #print(o2)


select_objects_in_modifiers(bpy.context.active_object)