Curious what led you to think that disabling Non-ASCII characters would fix Crittercism's handling of DexGuard-obfuscated stacktraces? AFAIK they would need to use the ReTrace.jar that's part of DexGuard not ProGuard (sorry i don't know if it's possible to turn off Non-ASCII chars)
To me this seems like an issue with Crittercism, do they support DexGuard? I asked their support team (support@crittercism.com) ~1yr ago about DexGuard support and it wasn't even on their roadmap.
If you're not tied to Crittercism I know Crashlytics and Hockeyapp support DexGuard (it was one of the reasons I switched Crashlytics).
update
Randomly I came across this today. You can override DexGuard's default obfuscation dictionary and define ASCII only characters.
define in your dexguard-project.txt
-obfuscationdictionary dictionary.txt
-classobfuscationdictionary classdictionary.txt