For example, a login to the Administrative UI is considered a login, but it is also considered a UI event. So when you log into the UI, you will see that in the smaccesslog4 and the smobjlog4. The smobjlog4 only has an entry for sm_objname and sm_objoid if you are dealing with a specific object in the UI, like creating a realm, or deleting an agent... A login to the UI will log a row into the smobjlog4, but it will not have sm_objname nor sm_objoid.
What is the signification of smaccesslog4 table's fields: sm_categoryid, sm_eventid, sm_reason?
You have a description of all fields of smobjlog4 and smaccesslog4 tables in the Policy Server Administration Guide r12.0 SP2 at Appendix D: Log File Descriptions
Does this mean that it stores all Administrative UI actions made by administrators?
Yes, the old Administrative UI and any admin API commands would be logged here.
Does the report called "Submitted Tasks" logs the same the smobjlog4 table?
No, the Administrative UI submitted tasks uses the new inbuilt RBMS in the Administrative UI itself.
Does the report called "Submitted Tasks" reads its data from the smobjlog4 table?
No, its uses the inbuilt data.
What is the difference between the smobjlog4 table and the "Tasks persistence" table of Administrative UI?
One is the admin access for the policy server and the other is the admin tasks executed fromt eh Administrative UI.
sm_categoryid and sm_eventid field in smobjlog4 table logs values like 100, 601, 106, 107, 108... Can we have a list of the meaning of each values > 100?
You can get more information in the /sdk/lib/smEventApi.h provided with the SDK. For example: