Warning: This post contains graphic pictures of very large insects. Bug-phobic people should look away.
Though, on whether or not rhino beetles are harmless, I'm actually finding conflicting reports. These guys are probably Ox Beetles, Strategus aloeus, because that's the only species of rhino beetle I've ever actually seen in person around here, though theoretically we could also get some Eastern Hercules Beetles (which I more commonly hear called "unicorn beetles"), Dynastes tityus, which are even more impressive. Daniel said he's seen a couple of unicorn beetles around, and found a dead one he has pinned in his bug collection (don't worry, he only collects already-dead bugs). Most people around here just call the Ox Beetles "rhinoceros beetles", even though technically they're just one certain species of rhino beetle, probably because they're the most common one.
According to Howard Garrett's Texas Bug Book (which is a good book, by the way), rhinoceros beetles are harmless detritivores that live in gardener's compost piles. He even has a picture of one on the cover! Texas A&M also says they're "Not generally considered a pest." However, Wikipedia says they're a pest and eat plant roots.
Well, I guess that just shows you that you can't believe everything Wikipedia says. I think I should trust Texas A&M. So far the only rhino beetle grubs I've ever seen have been in my compost pile, or in piles of rotting leaves like these. Even if they do eat a few live plant roots, which I seriously doubt, the adults are just so darn cool looking, that I wouldn't kill them anyway. So I hope these guys make it, and this summer I get to see some adult Ox Beetles marching around.