UPs are fine to create, as they likely contain legally defined boundaries. The only reason they may not be incorporated is because they do not meet the State's land/and or population requirements.
CDP's on the other hand, do not have legally defined boundaries, and are defined by the Census Bureau for statistical purposes (and are subject to change with any census).
As an example, I live in a CDP. The boundary for this CDP has changed with every census, but generally does not cause any issues since we are a rural community and the boundary expands as the area does. It is like adding onto a house... Still the same house, just growing!