Sorry for the slow answer. For the Discovery board the MIDlet should autostart automatically, but I have asked one of our experts to get back to you on this.
Sorry for a long response.
Yes, it's possible to configure an IMlet in a way that it will be started every time the board is powered up.
To achieve this, please add the following property in IMlet's JAD file
and re-install the IMlet.
The property may be added manually by editing the JAD directly or leveraging NetBeans.