Presuming you already have 8 speed Ergos and a matching derailer you want to use on this project, a much better plan is to just use a standard non-Campy 7-speed freewheel, for a bunch of reasons.
As Batman pointed out, Campy 8 freewheels existed, but they're weird, rare, and probably expensive. Campy 8 cog-to-cog is 5mm whereas Shimano and everyone else is 4.8mm, which is a big enough difference to make it not work so great, even indexed off the middle.
8-speed freewheels of any brand suffer from the issue of greatly exacerbating problems with bent and broken axles because of the amount of unsupported axle they require. Conventional wisdom has become they either push past the limit in this regard or come close to it. Dealer-level bike brands have rarely specced them for this reason - there were a few years, say 2000-2002, where some bikes at low price points had them, but there was backlash. Axle problems are just very common with them.
So, another approach you could take is just use a 7-speed Shimano or Shimano-compatible freewheel with your Campy shifter/derailer. The spacing is 5mm, exactly what they expect (Campy 8 kept with 5mm and began requiring a more severely dished wheel). So you'll have one click locked out, no big deal. And the freewheel will be cheap and work well, instead of a vintage part.
With either 7 or 8, you will probably have to set up your hub and wheel for it in terms of dishing and axle spacing.
Another approach would be to use the Hubbub mod with your Ergos on a Shimano derailer with a 1.7mm actuation ratio, which gets you into the right amount of derailer movement for a conventional 5/6speed freewheel, again with some locked out gears. That way if you have a vintage hub/wheel and don't want to bother respacing/redishing, you can just put the the freewheel on and go.