For the sake of "management purposes", people will have the SAN guy set up different "drive letters" so they can more easily keep track of their data files, log files, and do some cool things with TempDB.  On a SAN, that's normal "just" all logical junk.  It's a very rare thing where the logical "drive letters" actually match physical drives. 

So, yes... go ahead and do the separation of different files/uses by drive letter.  Just understand that there's not going to be a performance improvement because you probably won't be talking separate drives just for your drive letters.  And, other systems are also sharing those same disks so the chances of you have 1 or more physical drives dedicated to your drive letters falls somewhere between slim and none and slim just left the building. 😀