I have Brother DCP-7065DN all-in-one hooked up to my Buffalo WHR-G300N router, which is running a recent (though not quite latest) build of DD-WRT, using an ethernet connection. For computers accessing the wireless network, the printer is visible as a normal network printer and will happily print on request.
However, if I attach a computer to the router via ethernet cable rather than via wireless connection, the printer is no longer visible to that computer on the network. As a result, I can perform network printing if and only if I'm on the wireless network – not when I'm on the wired network. This is at most inconvenient, but it is extremely perplexing.
I've tested and confirmed this behavior from two Macs – one running 10.8.2, one running 10.7's latest – and from a Windows PC running up-to-date Windows 7.
Brother tech support simply pointed me to their normal walkthrough documents, which were not helpful.
I can supply any data from the Buffalo router's settings, but don't know which pieces would be useful.