Printing to .ps (or directly to PDF, which automates the .ps to distiller part on Windows), is the only way you will get composite gray directly from InDesign CS5, but it isn't foolproof. Make sure you have your Appearance of Black preference set to Output All Blacks as Rich Black or you'll wind up with dark gray screened type and other 0,0,0,100 elements. When you output blacks accurately during a conversion, 100% black is reserved for 4-color rich blacks.
