The vertex centric index is written to the storage backend, so I guess the section on write performance configs should be relevant:
https://docs.janusgraph.org/advanced-topics/bulk-loading/#optimizing-writes-and-reads

If have no idea whether row locking plays a role in writing the vertex centric index. If so, the config properties you mention are relevant and maybe also the config for batch loading, which disables locking:
https://docs.janusgraph.org/advanced-topics/bulk-loading/#batch-loading

Id allocation does not seem relevant (it has its own error messages so you would notice).

Marc