Recording device detection sounds too weird for me, specially in a console. I've seen VHS footage of DC games before, so it obviously doesn't have such fancy protection. I also believe it's not that possible to "detect" recording devices - the most I saw on anti-recording schemes involved sending signals that can confuse a digital timing device (capture cards, not-too-old VCRs), and causes image and audio to go out of sync, at best (it can be really annoying).
I'll say: try using another cable, preferrably a standard RCA, and see what happens. Maybe the VCR and the TV card are not generating enough current for the DC to activate the output ports, or something like that...