Yes they can.
and people has done that. http://ermau.com/using-winrt-from-net/
Interesting, I'm sure the opposite was said during the keynotes, but I'll take that as a more authorative resource. Still the majority of the really neat stuff like charms and contracts will presumably require appcontainers so I'm not sure there will be quite the same benefit (although .NET developers will probably be glad not to have to PInvoke quite as much).