That's really funny...
So, what you supposed was wrong, probably you were confusing the names of some archived BNDL or EMBB file with the TOC of the LTAR archive (the only one with underscore->path fix).
BUT while I was checking some LTAR archives here (yeah I ever verify what the users tell me) I noticed a sort of directory tree located after the file entries, luckily wasn't too hard to parse it.
Long story short: the filenames are only filenames without any folder separator, that explains why you were wrong with the image you pasted (it's impossible to have a full filename like "characters\modelcharacters\player\bodies\bodycelebrimbor\player_celebrimbor_quiverwraithproxy.mat") and I was wrong by using the underscore->path fix (maybe was it necessary in a very old version of the archives?).
Script 0.4 http://aluigi.org/bms/shadow_of_mordor.bms