Hi,
I do not know your type of video scrambling, but as a rule in analog systems they are changing sync pulses and positive/negative polarity of modulation. As a result there are problems in TV-set to receive this signal directly without distortions in IF/demodulator for some error in AGC. To avoid this you need special circuit to catch AGG level during VBI and hold it for all frame. So, you need at least changing of rx stage in your VCR.
Suppose you get videosignal directly from decoder demodulator. You will face other problems: VCR needs clear sync pulses to write signal on tape. You will get scrambled signal with non-standard sync pulses. So, your VCR will not write this signal correctly, and you will have no possibility to playback this signal again.
Other problem is that your SVR possibly is not writing information during VBI, so it will not write digital access code even if signal would be with standard sync pulses.
73! klug.