How bitcoin application in production retrive UTXO's AFIK, UTXO of an address cannot be retrieved using bitcoin-core, without importing the address in the wallet. 


How are application in production able to get UTXO ?
Does all the application use Indexed database like Insight or Abe to get UTXO ?
Is there any way to get UTXO from bitcoin core without importing the address into the wallet?
Most services operating large scale wallets only use Bitcoin Core for networking information, and maintain a separate utxo set for wallet purposes.

There are many existing options to build a full utxo set that can be queried for arbitrary addresses, such as the insight project.

Moreover, recent versions of Bitcoin Core come with the scantxoutset RPC call, which allows you to locate unspent outputs for a given address or locking script.