I just tried the demo and got it to work without problems. Renoise showed up as ReWire devices in Podium without even starting it first. If they don’t appear, try using the ‘Update ReWire Mappings’ option from the devices menu (the button above the devices column on the project start page).
I know this is a problem with Ableton Live, for example, but I think you don’t have to run Renoise separately. Just try running Podium, drag some of Renoise’s ReWire device mappings to the tracklist and power the arrangement on, and Renoise should start automatically!