It depends on your pool..
mmpool.org will take multiple machines with one worker name. I use 4 sp20's on the same worker name.
also
kano and ck the writers of cgminer have the pool below I have combined multiple machines to one worker with them.
https://bitcointalk.org/index.php?topic=789369.0I've also done this with ghash.io, it seems to work as well.