A shared attitude between the UX designer and the developer is not only healthy but necessary. Both of them have to focus ultimately on what the users will get, and use. It's not about having the fanciest, most unique and innovative user interface. Nor is it about having the most whiz-bang technology or groundbreaking coding techniques. It's about having a software that will be easy to use, useful, and usable. "Easy to use" because the user interface is intuitive. "Useful" because it does what users need it to do. And "usable" because it works when users need it to work.
The UX designer should be able to explain and illustrate adequately to the developers how the software works, looks, and feels - whether that would entail showing a functional spec, wireframes, or a complete set of mockups would depend on the maturity of the developers, and the ability of the UX designer to explain. But as long as the developers do not fully understand what the product is supposed to be and do, then you will always have problems along the way.