AFAIK, fields are usually considered an implementation detail and are not part of the API. So your code currently works and will likely continue to work for a long time, but technically it is possible that some future version of Julia changes the internals of zip and your code breaks.
I would recommend that instead of passing a zip() object, you pass a tuple of iterators and then you only zip() them once you start iterating.
N = 3
it1 = fill(1, N)
it2 = fill(2, N)
iters = (it1,it2)
# Do what you need to do with iters[i], then iterate using
for i in zip(iters...)
# Work on i
end