Sadly not technically.
Im not really sure about the capabilities of diskaid but i think i know what its main putpose is. You can probably change the .png files but as far as half of winterboard themes go, they wont work. Semi-so to speak, Jailbreaking lets anything that is 3rd party, have access or modify your system files and thats what winterboard does. Not just the custom png files that make up a theme.