Dtrace script newproc.d stopped working after upgrade, because of missing proc:::exec-success probe
This is probably because of the "Rootless" feature in El Capitan.

You can disable this feature by rebooting into recovery mode and running the command csrutil disable (and you can similarly reenable it with csrutil enable).

There is a great explanation over at this Ask Different question: What is the “rootless” feature in El Capitan, really? The second answer addresses Dtrace directly.