How to auto-start X/graphical programs in xmonad upon log in through kdm on Fedora 20
 

Solution:
xmonad-start checks for a '~/.xmonad/session' file and runs it:

if [ -r $XMONAD_DIR/session ]; then
sh $XMONAD_DIR/session
fi

or alternatively :
either put a check in /etc/X11/xinit/Xsession
like

# GDM provides either a command line as the first argument or
72 # provides 'failsafe', 'default' or 'custom'. KDM will do the
73 # same at some point
74 if [ "$1" != "default" -a "$1" != "custom" ]; then
75 if [ -f "$HOME/.xprofile" ]; then
76 . $HOME/.xprofile
77 fi
78 exec $CK_XINIT_SESSION $SSH_AGENT /bin/sh -c "exec -l $SHELL -c \"$1\""
79 fi
80 ;;

and optionally refine for also checking against $1 being xmonad-start