I'd guess it depends on the drum.

If it's a chrome over Ludaloy Ludwig, maybe a Super Sensitive or Supra, pits are a given. My Super Sensitive ('62 or '63 vintage) has pits about the size of pinheads on it and it doesn't affect the sound at all. As a matter of fact, it's replaced my '68 Acro as my main snare.

If it's a chrome over brass (COB), then it might point to the drum having a harder life and you might want to look past it. The chrome attached to the brass better, in theory, and if it's coming off it might be because of abuse or storage in a caustic environment.

It's a term that is used to describe the flaking of chrome off of a metallic surface over time.  This flaking often resembles little "pits" not unlike pockmarks in the plating.

Ludwig snare drums made of Ludalloy (aluminum alloy) are notorious for their vulnerability to this condition since you generally cannot chrome-plate aluminum with lasting success without priming the surface with a plating of another metal.  Even so, it may not take—as we all have seen.

Here is an example of "pitting" on a Plymouth fender.

Sorry about that--I never did well with two-part questions on tests in school.

If you're buying an old Ludaloy drum, make sure you can hold it in your hands before you buy it to see how bad the pitting really is. I probably wouldn't have bought my Super off of e-Bay, but being able to hold it in my hands at the music store, I could see that the pitting was minimal. Be careful buying chrome over Ludaloy drums off the web.