I'm sure LFM could tell us more about how these things work but I can't imagine it's likely that Onstad would actually end up doing the voice.
I read something in the Wired article that he really wanted to find someone else to do the voice. Found it, "DiGregorio voices Philippe while Onstad takes on Roast Beef himself, though he hopes find someone else to voice the character in the future." Apparently Huss is already a done deal for Ray, Onstad likes him that much.
I'm not really knowledgeable about the voice talent industry, but Onstad used professional talent and I'm pretty sure they would have been paid for the pitch. He is working with a Emmy-level producer, Josh Lieb, so I would imagine that if he brought his A-game and hired good talent for the pilot or test footage, the studio execs would be more receptive to picking him up. I would imagine the voice actors would get a contract if the show gets picked up, and if the show blows up they would be able to negotiate really high salaries for themselves like the voice talent for the Simpsons did.