I have a few applications that do not show icons in kmenu. I have placed icons in both /usr/share/pixmaps and in /home/billydv/.icons for the application but to no avail. Is there a way to get kmenu to recognize this automatically for any user? I know that I can specify the icon with menu editor but I was hoping for something more permanent that would show up automatically for all users.

You need to place them under /usr/share/icons/hicolor/<icon size>/apps/

When I do so do I need to update the cache file?

I'd say so. (I am not sure it's absolutely mandatory but I'd do it all the same).

Usually running kbuildsycoca4 followed by restarting the application involved will be sufficient to refresh the icon.