Actually...that is an ideal, but in practice it is not true. The word in question "güero" is rarely, if ever, pronounced with the /g/, but as if /huero/.
This pronunciation theme is pertinent in this slang forum,too. So much slang comes from shortened or mispronunciations. Heck, it can even lead to qualifying as an entirely other language. (See some of the pronunciation differences between Spanish & Portuguese, for example.)