Deepak,
Using the snmpcollector Query Discovery Server pulls device discovery info obtained by discovery_server and stored in the UIM database into snmpcollector local db. From there snmpcollector polls the devices and builds the inventory tree for each profile, which is added to the local snmpcollector db.
As Phani explains there is no sync function possible for SnmpCollector.mv.db and the UIM db.
If profiles are manually created then the info exists only in SnmpCollector.mv.db.
Also it is recommended to have regular backups in case it becomes corrupt. Yes it can be rebuilt via Query Discovery Server but restoring the backup may ensure less down time.
Yes, you are correct all the qos and alarm messages generated are sent on to the primary hub for processing and none are saved to the local db.