RGB video ADC for oscilloscope?
This ADC is designed rather specifically for use in a video digitizer application. It is unlikely to work well in other scenarios. (Additionally, Analog has declared the part NRND -- Not Recommended for New Designs -- so it is a poor choice for a new application anyway.)

The biggest problems you're likely to run into have to do with blanking intervals.  It's not clear whether the AD9883A would operate correctly without some sort of regular sync input. More importantly, the ADC is designed to accept capacitively coupled inputs, and self-zeroes during horizontal/vertical blanking intervals. A static or slowly changing input would not be digitized properly.

If you just want a high-speed general-purpose ADC, Analog has plenty of those. There's no reason to try to shoehorn a video ADC into this application.