I have gone through the blogs, docs, tutorials (links below) and concluding that ACID transactions works with Internal Hive tables with ORC format. They do not work with External Hive Tables. Please let me know if I have misunderstood and there is a way to make ACID transacitions work with External Hive Tables.
The general thinking is that external tables are not owned by hive and files/folders can change outside of hive's control. You can't really provide transactional guarantees under these circumstances, which is why the restriction is there. Do you really need to mark those tables external? Can you just convert them to internal?