Here's how Warden works:
It checks specific addresses in the client's memory for a value it expects (for example, Lua protected functions). If that value isn't EXACTLY what it expects, it automatically bans the user. Easy as that.
So unless they SPECIFICALLY add a Warden check for the memory address that is modified in this WoW.exe, Warden CANNOT pick it up. Of course, you can also whitelist that specific address. That might open up for malicious activity though (unlikely, but possible).
This is the same reason that hacks modifying non-public values in memory (as in, those that you can't find all over the internet) are generally very safe - because the owners of private servers don't know about them UNLESS they do some digging to find them themselves.