Both Mainland and Ohana are merchandising businesses. Their business is selling ukuleles, not making them. You need to stop getting the manufacturing and selling mixed up. They both order product from a foreign factory and get their brand put on the product. It matters that the factory produces good quality, but it does not matter where or what the factory is.
The people who own Ohana and who work at Ohana are just as local as the people who work at Mainland. The difference is in how they operate their merchandising business. Mainland is based around a physical shop operated as a family business, Ohana is a larger sales office distribution arrangement. So you get a different front of house service from each of them. But that does not mean either of them is more "local" than the other. Their workforce is employed in the USA, their workers get paid USD. Except the agents in other countries.
You can be sure that the factory owners hide their whereabouts and operations from the end buyers for a reason. It may be a good or bad reason. If they thought telling you about the factory could get more sales you would know all about the factories. The assumption is always that they want to hide poor treatment of workers or environmental issues. The reality may be that they may want to hide the fact that the machines are also used to make wooden stocks and parts for military weapons, it may have nothing to do with workers or the environment. We have no idea and those who know have sold out and locked themselves into confidentiality agreements.
Going back to Ohana vs Mainland, it depends what you are looking for. Each of these merchandisers has a different product range. Their target markets are not exactly the same. Look for the features you want, not the brand name.