Hi Chris,
I work with LT/RT Mixes almost daily in FCP. Hopefully I can Help you out.
the file will appear as stereo. as you mentioned the the file should be hard panned already.
1 make sure that your track is set to stereo pair.
modify menu>stereo pair
2 audio outputs should be set to stereo pair.
this is important. if set to mono outputs the lt/rt mix will decode properly off the FCP timeline,
however upon playback the file created will collapse to centre channel.
in regards matrix decoding, the original format of Dolby pro Logic only decoded a mono track for both surrounds, in the greatly improved Pro Logic II format of matrix encoding/decoding each surround speaker has seperate information. the end viewers home theatre system equiped with PLII will derive an LFE track for your sub . giving a 5.1 listening exoerience.
Granted this is not as discrete an experience as Dolby Digital 5.1 (ac3 file)
Dolby Pro Logic II is considered an acceptable delivery format of 5.1 surrpund sound by industry professionals and broadcast houses alike.
CHeers
Ryan.
Ryan