It's not the configuration.... It's the fact that it is powered by a dimmer... A switched outlet is one thing, a dimmed outlet is another. By proxy it becomes part of the lighting system. Plug a vaccum or a computer into it and it may not be so nice. As it is not usable as a 15-20A outlet, IMO it does not count as one, it is a lighting outlet.... As the cord cap for them is described here.
http://www.lutron.com/applicationnotes/048085b.pdf "The DFDU and HFDU receptacles with the RP-FDU plug are UL listed for use with
specific Lutron dimmers for the control of portable lamps."
However a 1/2 dimmed would....
