Hi Marcio,
I do understand that the fact that Auto-Activate is off by default for spawnable particles seems a little bit hidden. However, the tool, in general, is meant to take care of setting some variables to an expected(for sequencer) value for best performance. This is especially true with spawnables. Sometimes variables in a spawnable are expected to be off because we are giving users the most control over the actor through sequencer(i.e. the toggle track).
In the case of the particle toggle track not working, you must toggle on or after the frame that you key it to be spawned. If the particle is unspawned, triggering it will not have any affect.