American here. Having lived most of my life on the Ontario border, hearing “zed” for “zee” is nothing at all uncommon. I can’t think of a single acquaintance that wouldn’t understand “zed” (i.e., no Zedimmermans here). As an engineer (and ex-soldier), I’m always very careful about properly pronouncing “zero” instead of “oh,” and depending on the context, I often find it useful to say “zed” instead of “zee.”