I tried doing that online with the horse racing track in the deathmatch creator, had a few car ramps set up and all, but I couldn't find the truck in the off-road vehicles. I'm not sure if I had to buy it first, and then it would be available, but...it wasn't in there for me.
As far as me buying it, I think I'll pass on it. Yeah, it looks cool, but it doesn't quite drive as well as I'd hoped. Still gets stuck on cars, not very fast, and the price is way more than I have, considering I blew all my money on the Hipster Update. I think I'll just tinker around with it in single player, where I believe it will always be available, since I still have the Roosevelt.