Using only video output to connect to the switcher (chroma key usage)
Some production switcher are more mixers for video content. They have limited number of inputs, and you cannot configure an external CG's video / key inputs. If this is the case, you will need to use the chroma keys feature of the switcher in order to create a key channel substitute. (A chroma key will take out all the black areas of your graphic and make them transparent.) If this is sufficient, then this option might work.
If you have no available inputs for a key channel but would like to keep the original transparency, place the Compix system downstream from the switcher, so your switchers PGM would go through your Compix system.