In order to have Oversec correctly process what's shown in in the Hangouts app, you need to enable the option "Scrape All Views" in the "Lab" tab of the Hangouts-specific settings in Oversec.
Please do not attempt to use PGP Encryption with this app. PGP Encrypted messages are BIG and will need dozens of SMS to transfer. Moreover, The Hangouts app is known to crash occasionally when PGP encrypted messages with invisible encoding are fed into its input field. More Info