I gotta agree that those don't look like they'd make good jumps, I'd be worried about getting a hoof caught.
Instead of using them for actual jumps, you could use them as standards. If you can find a way to attach jump cups. Just a suggestion.
No, they would not make good jumps. The slots between the jumps are too big. They also do not look like they have enough support to them.
Your better bet is to either purchase some lumber off craigslist that was bought to build something, but was extra....as well as some wood lattice from your local home building center. Build a simple frame with "feet" and attach the lattice to it.