>> 1) SnapManager for Oracle creates online backups/snapshots of Oracle database (i.e., inconsistent Oracle backups)
SnapManager for Oracle (SMO) will put your active database(s) in backup mode (alter database begin backup) prior to taking snapshots of your data, and take your database out of backup mode afterwards. Hot backups require the database to be in archivelog mode.
SMO can also take a cold backup if you so desire, and can shutdown/restart the instance for you if you wish.
>> 2) After restoring a backup (from a snapshot) I would need to perform media recovery before I can open the database for operation, becaue of the backup is not consistent
Restoring a cold backup would require no recovery.
Restoring a hot backup always requires recovery. If you have all of the archivelogs available (from the time of the backup up to current), you can recover to any point-in-time or SCN between the backup and now. SMO will do all of this for you, or let you handle the recovery yourself.
>> 3) I cannot revert the dabase to the point when I last performed a backup/snapshot without doing media recovery, i.e., a snapshot can not be treated as an offline backup
If I understand this question correctly, yes, you can revert the database to the point-in-time of the snapshot, without media recovery, if you perform a cold backup (shutdown instance, snapshot, restart instance) and are restoring from it.
Hot backups require recovery to make them consistent. This does not mean that every archive log needs to be applied - you can still recover until a specific point-in-time or SCN, or manually. Often only 1-2 archived logs need to be applied to make the database consistent, applying more is up to you.