C++ is an ANSI standard language. There are standards that companies can follow to implement the language. C++ isn't a different language in different IDE's...
BC++ (Borland) is different from Visual C++ in that they use different compilers and libraries. There are standard libraries out there, and then there are the add-ons that each manufacturer supplies with the product. VC++ is geared more towards ATL and MFC development on Windows.
BC++ has its own IDE called C++ Builder. Can you use the BC++ language in Visual Studio? Kind of, I believe you could manipulate the settings such that it redirects to the BC++ compiler.
Can a VC++ person work in BC++? Yes, its C++ after-all, the only difference may be some libraries that are supplied. VC++ is not geared towards .NET, although Visual Studio can develop in a different kind of C++ called C++/CLI for .NET, and Borland can't.
Microsoft does not provide an IDE for Borland. That would be like Ford providing steering wheels for Chevrolet.
Not sure what you mean by back-ends for BC++.
Edit:
Here is the newest version of Borland C++, which now has a different name:
http://www.embarcadero.com/products/cbuilder[
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