Is there a way to read the data from the chat messages in DM or Group with out adding the bot the DM or Group?
Similar to the APIs that are available to programmatically access the google drive, is there a way ?
No, there isn't.
The only API access you can get for Hangouts chat rooms is by using a bot. You can also use a webhook, but this is only for sending messages and not receiving.
You will need to use a bot to be able to do this.