An Elisp regexp can't express this, AFAIK. (Some regexp dialects can.)
But you can do it in two steps:
Mark oil matches, which will include some wip matches.
UNmark wip matches.
There seems to be no command image-dired-unmark-tagged-files. But you can define one, just by binding dired-marker-char to a space char and "marking" with that. Like ...