Actually, it considers it RAM when it's Data memory, ROM when it's Code Memory. Of course if you perform common write with MOVX to a device that requires, say, special write commands (i.e. it uses a "command register" to perform write, read, verify, erase etc separately, and requires "erase" before "write") it just won't work.
In short: As long as -you- treat it as ROM and don't try writing to it, it all works just OK.