Campagnolo ten speed with a vintage derailer

Maybe it has more to do with the rear sprocket & the index shifter in the brake setup.
I did see a video with a ten speed campy chain installed on a vintage derailer.

I presume you mean front der since you talk about it with a crank. It might depend on the vintage of der you have in mind, and at the end of the day, you'll probably just have to give it a try to see if it works well enough for you. The cage for let's say a 10sp front der might be too wide, such that the crank arm will collide with the der cage when shifting into the big ring and might need a good chain catcher to prevent the chain dropping off the inner ring when down shifting. That all assumes friction shifting the front der. I can't imagine too much joy trying to get a Campy 4 click index shift lever to work properly with a front der that has the incorrect cage width or possibly different cable throw.

These parts ten speed Campagnolo have been together for years, three bikes.
many years on this Serotta. I just installed a new chain, the alignment of the rear lower cog of the rear derailer was not centered. Hence chain would grab each tooth of the cog, eventually I figured this was an alignment issue.
the old chain was so worn did not matter evidently but a new chain did not like it.
so I had to give enough force on end of rear derailer to get it back in proper alignment.

Now it sounds like you might be talking about the rear der. Still very unclear what parts you are trying to mix. Have you aligned the rear Der dropout? If chain got badly worn, you will almost certainly need to replace the cassette too. New chain on worn cassette will cause problems. If you are talking about replacing the rear Der with an older vintage, then you are very likely to have indexing problems as cable pulls have changed over the vintages, and potentially issues with the width of the Der pulleys.