Yes, it is already working for vanitygen. It seems to be not working in oclvanitygen (I found this thread searching about that.)
Example litecoin litecoin addr: vanitygen -L LiTe . Namecoin: vanitygen -N NC . Any other coin can be done with the -X flag that lets you specify a version code (though it may be a bit of work figuring out what your coin's version number is.)
Actually it is not that hard.
Just go to the source files and look at the Base58.h file.
Around line 280 on most coins, look for the constant PUBKEY_ADDRESS being assigned. That would be the address version you need.