Please notice that publish/unpublish push API only work for Wowza servers, you can't setup it for Nimble. You can use publish control API instead ( https://blog.wmspanel.com/2015/12/rtsp-publish-control-setup.html ), but it will be called on start on publishing only.
This API is called from Nimble instance, so it would work even without WMSPanel access.
Also you can call
/manage/publish_control/status API on Nimble instance directly to poll status ( check https://wmspanel.com/nimble/api#toggler=14 for details).
There are no notifications for other protocols, you can only pull stream status via /manage/rtmp_status API ( despite of name, it return status of all streams) and check when bandwidth would change from 0 to some value.