I've been running RC drop brackets for over 3 years now. Never had a problem. I actually didn't even have the reinforcement brackets bolted to the frame. They were just on there. That was until just a few weeks ago anyways, when I welded the brackets to the frame. Never liked the sound of drilling holes into the unibody for four self tapping bolts that are going to be sustaining a lot of force. Maybe I'm just underestimating the thickness and strength of the unibody, but I'd rather be safe then sorry. So I just waited till I felt my welding skills were up to par, so I could be confident in the strength instead of having some ugly welds and no actual holding power.
Get great flex and haven't had a ground clearance issue yet. I don't really see any issues to come either. I figured if they ever did get hit, I would rather it be them instead of the actual arm itself. It's probably not gonna even harm the bracket. Apparently hitting the long arms isn't an issue either though, because I don't recall ever hearing anyone mention doing it before.