Yes it is possible. One code set, one database, two (or more) sites.
Two possible approaches ...
Firstly there's a multisite add-on somewhere in the downloads area that I believe works by separating products for each site into categories, which I guess you could then cross-link between (we've not actually used this mod at kuroi).
Second approach (which we have used) is much more technical and requires a fairly high degree of techncial knowledge of Zen Cart's internals, though the changes themselves are fairly surgical. You'd need a new table (or an extension of the existing product table) to indicate which products were available to which site. Then the listings and search pages algorithms need tweaking to restrict the products displayed to those that are appropriate to the site - we re-wrote the misnamed "hidden wholesale" add-in module to allow this. Then there are admin changes to allow whatever data structure you've implemented to be maintained on the product pages (we actually customised the quick updates add-in to do this).
We took it further too. So the tax treatment is different between the sites: the client has a wholesale site which shows prices ex tax and a retail site that shows them inclusively, which was done by hijacking the display with tax constants and setting them according to the site URL. We also recorded the where the purchase was made in order to brand invoices accordingly. And topped the whole thing off with a multi-domain SSL cert to avoid nasty warnings in browsers.