I don't know, I don't recall if I've ever 'captured' a cyberdisc, but I think I have. I know you cannot pick them up, so if you manage to knock one out without destroying it, you have to finish the battle to take it. If it's only achievable as a Get One Free deal, keep getting Academy people, probably some Marsec or Osiron might as well. Especially Academy Engineers would be the most likely.
Remember, if you really need to check, go to the Geoscape, press Q, then Q again to search, and type in 'cyberdisc', and it will show you every research topic with cyberdisc in the name. Click on each in turn, and you can get a list of what's needed directly to research, including a list of prisoners you can get it for free from.
Just note, the Academy Engineer has a lot of GOF articles, including a few unique ones, so to start out your chances of getting any particular research from them is very low, and takes a long time to increase those chances.