We have installed Ultimate on a new domain and want to import products from an old 2.2.3 install. We do not want to create an additional storefront from the old domain into the new Ultimate install. Instead we just want to import all of the products/images/global options. Is this possible with the store import tool? Or will I have to upgrade the old 2.2.3 install to a 3.0.4 install and then export the products from the admin?
That's what the store importer does: it imports a 2.2x store into cs-cart ultimate. All it's pages, products, etc. After the import you will have 2 stores. your old one, and the one on ultimate.
You can of course delete your old one - if the import has gone correctly, which is not always the case, so check this well!