After doing more research it appears odata4j which the vcac plugin uses to implement odata access doesn't support batch updates.
The processes we're trying to manage ended up being too complex to try to encode without batch updates and some of the other niceties available in the .NET vcac clients. We've ended up implementing an asp.net webapi app to expose the operations using native libraries and then plugging into that via the rest plugin as a workaround to get access from vco.