Is the /3GB switch supported on Windows Server 2003 Standard Edition?
It depends on what you mean by "supported". Unfortunately, the word has multiple meanings, and the intended meaning is not always obvious from context.
One definition of "supported" is "The software makes a good-faith attempt to implement the functionality." For the purpose of this discussion, I will use the word "implemented" to describe this sense of the word "supported".
Another definition of "supported" is "The functionality has been tested to a high enough degree of confidence that the product support team will help you if you have problems with it." I don't have a good word for this concept; I will use the word "blessed" for lack of a better term.
In the vast majority of cases, the product teams keep the two concepts in sync. If the test team won't bless a feature, its implementation will be pulled from the product. The /3GB switch is one of those odd cases where implementation does not match blessing.
Windows Server 2003 Standard Edition does implement the /3GB switch, but its use is not blessed. (It is blessed for Enterprise Edition and Datacenter Edition, however. See the linked article for more details.)