Currently there is code in insertDocumentForBulkLoader that checks for when replCoord->isOplogDisabledFor(...) returns false, here.

I looked for callers of the insertDocumentForBulkLoader function and it seems it's only called from CollectionCloner, which is only used in initial sync. So that means that there won't ever be a case where isOplogDisabledFor returns false, as the oplog is disabled during initial sync.

A patch with the following added to it ran successfully:

invariant(replCoord->isOplogDisabledFor(opCtx, nss));

So we should be able to simplify that function since we are sure that it's only called in the initial sync context (for example, we can remove the check linked above).