Asynchronous batch commits in Oracle
I went ahead and opened an Oracle SR, and this is what Oracle had to say:


  1) Do the batch commits span multiple connections?


No. Oracle will write data from Buffer to redologs once sufficient redo is generated by the session. Since your session is closed Oracle will write it immediately.


  2) Is there anyway to find out how often the batched commits are
  written to disk and become "durable"?


No. I have checked all oracle Documents and Metalink but that information is not available.  The most advanced documentation about Asynchronous Commits is available from this link.


  3) Are the batched commits written to disk serialized?


From what I understood from the documentation, they are serialized. Since transactions are written to Disk when "sufficient" redo is generated, I expect A will be written before B. Worst case they will be written at the same time. Please note that this not true with Multiple sessions like "A" from Session 1 and "B" from Session 2.