Is the HPS Sentinel Solar Duty transformer used for zig-zag or autotransformer grounding transformers?

No, the Sentinel Solar Duty transformer is meant to be used as a low voltage grid tie transformer to correctly adjust the voltage between the solar inverters, energy storage, utility grid and/or facility, especially where a bi-directional feed is used.  HPS does supply zig-zag and autotransformer grounding but not under the Sentinel Solar Duty heading.  Grounding transformers are a different application than the Sentinel Solar Duty transformers.