High PIDs on up-to-date AIX systems are ok. I remember it was a problem (or could have been) on AIX 4.3.3? 5.2?, but it's too long ago to say for sure, sorry.
I have not yet seen so many zeros in vmstat output. Must not mean much but looks strange for me.
The <defunct> processes are really not a good sign. They are zombies, failures of the program.
You say that you have so many processes so that the maximum number of processes per user is hit. How do you know this?
Do you have your box tuned with the recommendations for Oracle like setting at least maxuproc=4096. If it is on the default value, it will be too low most probably. That could be related to the Oracle error messages you get.
Here is a discussion about it:
https://forums.oracle.com/forums/thr...sageID=3445541
But you also find it in setup/tuning recommendations for Oracle on AIX.
Beside all that you should also have a look at the entries in the Error Report of AIX (errpt).