Anything you can do in winterboard you can do without it. I use SSH exclusively and even just posted a thread on how to use LockInfo without Winterboard as well.
If you open up a .theme file you can generally see where each file is intended to belong. Then you just SSH or use MobileTerminal/iFile to place them in the right spots.
ALWAYS backup files before replacing them.
I like keeping my phone fairly stock, so I only swap out a couple icons and the battery charge image (I like the one that shows %s) and then I now use LockInfo. All without Winterboard.
I know people say "it doesn't slow down a phone" Well, it does. With winterboard my memory tends to be around 7mb free and now I've regained about 15mb. Dunno why it would be so serious, I quess I removed a couple MobileSubstrate plugins with it.
Short end of the story, YES. Winterboard DOES use more ram than SSH themes.