All these were tested with the launch command, "editor" in attempt to start up the editor. There may be other ways of launching them with a work around, but with the basic way of starting it up, these are what work and what don't work from my personal library of games.
Works:SAW works, but alas unofficial and missing some elements like Mirrors Edge, but still functional.
Brothers in Arms: Hell's Highway launches fine, not sure of functionality in the editor, but fist glance looks like it works.
Don't work:All Points Bulletin ignores it.
America's Army 3.0 ignores it.
Batman: Arkham Asylum ignores the start up command and just goes to the launcher.
Bioshock ignores it. (Technically not really UE3 anyways)
Bioshock 2 ignores it.
Blacklight: Tango Down gives the error, "Editor not supported in this mode."
Borderlands ignores it.
Damnation tries to start up, but crashes.
Mass Effect ignores it.
Mass Effect 2 ignores it.
Medal of Honor ignores it.
Moonbase Alpha ignores it.
Rainbow Six: Vegas 2 starts up the splash screen, but stops with an errors saying, "You are not running the editor from X:\Perforce, this may lead to problems. Please update your shortcut. The editor will be closed. If you have any question, contact Bruce Bellavance." Obviously an in-house dev notice which never got taken out.
Rise of the Argonauts makes the UnrealEd splash screen come up, but crashes.
The Ball gives the error, "Editor not supported in this mode."
So as you can see not many games, at least from my selection work. There are still a ton of games that can be tested if anyone has them, and they're on this list:
http://en.wikipedia.org/wiki/List_of_Un ... l_Engine_3Like I said maybe some of these have work arounds, but I've not researched into any.
Hope this helps.