The parallel cable shall conform with NEC 2014 Art.310.10 Uses Permitted.(H) Conductors in Parallel. (2) Conductor and Installation Characteristics. (2) Consist of the same conductor material.
The ACSR conductor is not specifically recognized in NEC and has to be insulated, in my opinion.
See art. 310.106 Conductors.(D) Insulated. Conductors, not specifically permitted elsewhere in this Code to be covered or bare, shall be insulated.
If the additional conductor is part of the same circuit as the original ACSR run, then you have a violation of 300.3(B).Is it a code violation to add another wire to an overhead ACSR run? And if not what would be your wire selection use or xhhw?