The reply from Apple on this question was: "Drive Setup is intended to initialize all Apple qualified internal drives and some removables. It is possible that other drives could be initialized using Drive Setup, however there is no official support for non-Apple qualified drives."
The reply for Power Computing was: "This has been a gray area for quite some time. Typically, Apple does limit Drive Setup to drives that Apple itself ships. However, on the IDE side, things are more wide open. From what I understand, Drive Setup has broad support for all IDE drives."