Is it necessary/useful to include the publishers in the list of editorial board memberships?
Unless you work in exactly the same area as someone else, you likely have no idea how good a journal is. For example, I know that the SIAM Journal on Numerical Analysis is good -- but is the Journal of Number Theory good? the Journal of Mathematical Sciences? But if I know that one of these is published by a professional society located in the US or Western Europe, then I can infer that it is likely a good journal; whereas if the journal is published by a company I've never heard of and that is located in Egypt or India, then I may have my doubts.

So, yes, I think it is useful to add the publisher.