As far as I'm aware, not directly. However, .resx files are XML, so you if you're comfortable with their syntax, open them in your favorite plain-text editor (XCode, BBEdit, whatever) and hack away.
Edit based on the update to the question
Nothing, as far as my Google-fu can find, currently exists to fill this need. However, .resx files are relatively straightforward XML, so if you have a Mac and XCode, you can probably whip up something with an NSTableView
that operates similarly to Visual Studio's in-box .resx editor for strings.
Now, it's considerably less trivial to support other resource formats (particularly binary data), but strings at least shouldn't be terribly complicated.
I wish I could give you a "proper" answer, but unfortunately, I simply cannot locate anything appropriate. I see many .resx editors out on the web, but all are for Windows. To get you started building something (I know this wasn't your intent, but it's likely your only answer), check these APIs:
If building something is truly not viable, your other option is to either virtualize Windows (using VMWare Fusion or Parallels Desktop), or to use Boot Camp and create a Windows partition. Then you can install any of the zillion and one .resx editors for Windows -- or even a Visual Studio Express instance, which will also contain .resx editing in-box.