I've never gotten an RUU to work while the bootloader is unlocked, on any HTC phone I've had. Relocking the bootloader the RUU works as designed. Also, the OTA updates from T-Mobile will not install with an unlocked bootloader.
You only need to relock bootloader when the phone is s-on.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?