I always thought that codes didn't matter in SCUUM? It's written to bypass all protection anyway, I think. I know that I've played Indy and Monkey Island 1 and II - none of which were cracked - to completion with no problems.
*Edit* From the SCUUM faq:
3.1) Copy Protection:
The ScummVM team does not condone piracy. However, there are cases where the game companies (such as LucasArts) themselves bundled 'cracked' executables with their games -- in these cases the data files still contain the copy protection scripts, but the interpreter bypasses them (similar to what an illegally cracked version might do, only that here the producer of the game did it). There is no way for us to tell the difference between legitimate and pirated data files, so for the games where we know that a cracked version of the original interpreter was sold at some point, ScummVM will always have to bypass the copy protection.
In some cases ScummVM will still show the copy protection screen. Try entering any answer. Chances are that it will work.