I would like to know if I can stream live via wirecast or any other similar platform when using a Blackmagic ATEM Television Studio and Blackmagic Media Express. I am using a Macbook Pro and a Sony NXCAM 5.
The things you mentioned are typically mutually exclusive. Wirecast and the ATEM TVS are both video swichers. You only need one or the other. You can either plug your camera into a video capture device (like the Blackmagic Mini-Recorder) and use Wirecast, or plug your camera directly into an ATEM switcher.
For streaming, which software you choose depends on what streaming service you are using. For example, Livestream.com will stream straight from the USB output of the ATEM TVS, no additional software / hardware required, while Ustream or YouTube will not. Wirecast can also stream directly to those services if configured properly.
In both cases though, Media Express is only for recording to your hard drive, and has no streaming capabilities.