Connecting to Yammer, Office 365, Google, or Slack is no different than logging in with Twitter or Facebook to Spotify or another third party product. All these connections are using the same standard way called oAuth.
oAuth is a trusted authentication method between applications. Yammer uses oAuth to let Recognize tell you who your users are. This allows us to do some pretty cool stuff in a secure way. For instance, in Recognize we can sync your users in Recognize entirely from Yammer. As far as posting to your Yammer wall, well that can only be done if that individual user authenticates with Recognize and allows us to do that. We can't be sending messages on behalf of any of your users - only the ones that explicitly say it is okay.
As far as security implementations, the only concern is posting to Yammer via Recognize if a Recognize account is jeopardized.
Luckily, we have security measures to make it extra secure. For instance, you can disable passwords with Recognize and force your users to log in with Yammer. This reduces the number of passwords where your staff could have their accounts jeopardized via third parties.
See our security overview PDF https://www.recognizeapp.com/recognize-security-overview.pdf