As far as I know, not directly. However, .resx files are XML, so if you like their syntax, open them in your favorite text editor (Xcode, BBEdit, whatever) and hack.
Change based on question update
Nothing as far as my Google-fu can find currently exists to satisfy this need. However, .resx files are relatively simple XML, so if you have Mac and Xcode, you can probably hack something with NSTableView , which works similar to the Visual Studio in-box.resx editor for strings.
Now this is significantly less trivial to support other resource formats (in particular, binary data), but at least the lines should not be terribly complex.
I would like to give you the "correct" answer, but unfortunately, I just can not find anything suitable. I see many .resx editors on the Internet, but they are all for Windows. To get you started creating something (I know that this is not your intention, but most likely your only answer), check these APIs:
If creating something is really unsafe, another option is to either virtualize Windows (using VMWare Fusion or Parallels Desktop), or use Boot Camp and create a Windows partition. You can then install any of the zillion and one .resx editor for Windows - or even an instance of Visual Studio Express that will also contain .resx editing in the box.