1. Currently, api/v2/Participant.php civicrm_get_participant (and I assume search as well) is expecting 'event_participant_id' for input parameter. Unless there's a good reason for this that I don't understand - this should be simplified to just 'participant_id'. (If you pass in 'participant_id' currently, the api matches ALL participant records - which also seems like a bug.)
2. The 'Unique Names' used in Participant.xml are misleading - they use 'event_' as a prefix BUT are actually properties of 'participant'. Also, one of the properties should have a unique name assigned since conflicts are likely going forward. I've listed the current naming and recommended modified naming below. Verify / modify any affected code after making these changes.
[event_status_id] -> [participant_status_id]
[role_id] -> [participant_role_id] (this is not a conflict currently, but we are likely to use roles for other objects going forward)
[event_register_date] -> [participant_register_date]
[event_source] => [participant_source]
[event_is_test] => [participant_is_test]