[Apple Watch] Can I use Cardiogram's continuous mode during a workout?

Yes! Both continuous mode and workout mode can be used at the same time. In fact, if you start a workout from the Workout app, you don't need to click the "Start" button on the Cardiogram watch app. The Cardiogram app will automatically pick up the measurements taken by the Workout app, and display it in Cardiogram (on both the Cardiogram watch app and the iPhone app).