It seems some models conflict... http://www.sussmanlifestylegroup.com/support/steamhomeiom.pdf
"Insure a suitably rated 120AV properly grounded receptacle with GFCI (Ground Fault Current Interrupt) is
provided for the attachment plug cap configuration."
And, "Do NOT install a GF1 (Ground Fault Interrupter) to this..." http://www.steamist.com/Downloads/pdf2/327.pdf
Not sure what to make of the second one, as it is an electrical appliance with metalic piping into a shower, or wet location. It may have one inside as part of listed equipment. Having two would trip eachother....
I have always followed 680 IV for these installs. Which is why I mention the GFI disconnect and bonding. If I have been doing it wrong all these years let me know. As it may be a local thing I have gotten used to, because my Inspectors always ask about the bonding and GFI for these.