A single Decklink channel CAN key over a live input without capturing into the PC. Live video to input > key overlay from application > Live video to output. This option can be demonstrated by the livekey utility that comes with decklink card, or in products such as Titlebox. Thus you can overlay graphics on a live video feed without capturing on one decklink channel, keying in software using CCG, and outputting to a second decklink channel.
Is there any way to use this feature of the decklink series with CasparCG, I only seem to be able to configure the damn thing to suck in video as a producer and output it as a consumer. It seems daft when the hardware is capable of doing a hardware ‘live’ key, that the CPU has to composite the production. The other beauty of using the Decklink hardware key you don’t get any latency on through the signal path.