Yes, it should work.

When you start Orange, the first thing it will do is look for `bitcoin.conf` in the default location. Based on `bitcoin.conf`, it will decide where to look for the .cookie file and Bitcoin Core RPC server, http://localhost:18332 (testnet), http://localhost:18443 (regtest), or http://localhost:8332 (mainnet). Then it will start communicating with the server and display the information on the UI. It shouldn't matter what network the server is using (I haven't tested using regtest though).

(I'm currently working on support for manually configuring the server URL and authentication: https://github.com/orange-org/orange/issues/19 This should be useful for users who have non-default configurations)