They can, or the IP. There's some specific DD-WRT builds that can do it by port on the router.
I don't know a whole lot about Tomato. When I got my WRT610N V2 it was only just starting to be supported by DD-WRT and nothing else. No idea on the status of my WRT320N, and I know the Valet M10s we use at the store have no Tomato support at all.