"Sharing only" account not visible in "Users & Groups" since Mavericks
I have had this issue as well and I found a solution:
http://support.apple.com/kb/TS4404 on the Apple support website.

Just type the following two commands in terminal:

Quit and reopen System preferences and the sharing account will show up:

sudo dscl . create /Users/root GeneratedUID FFFFEEEE-DDDD-CCCC-BBBB-AAAA00000000

and then:

sudo dscl . create /Users/accountname UserShell /bin/bash

Replace "accountname" in the commands above with the missing account name.