When you select someone as playing themselves, it says Him/Herself.
This is a very awkward wording when it actually shows up on the cast pages. Seeing a man or woman listed as "Him/Herself" seems kind of awkward.
I'd suggest the gender/neutral "Themselves" instead. "Themself" is also used in very informal language, but it's generally frowned upon in grammar guides. Such as here.
Seeing, for example, Bob Smith listed as Him/Herself looks... kinda strange. :)