I have no experience with the boat rollers, but I have towed various empty boat trailers, sometimes for fairly long distances, the longest trip being about 400 miles down from Scotland with an empty single axle galvanised steel break-back trailer for a 1 ton, 20ft LOA sailing boat, plus a trip of about 200 miles with a very light empty alloy trailer over Swallow boats to pick up my Winsome hull.
It's perfectly OK towing empty trailers, but they do bounce about a bit and can be a bit noisy on rough surfaces. Keeping the speed down helps, but generally the noise and bouncing doesn't seem harmful, it's really just a bit of a nuisance more than anything else. I found I had to stay at around 40mph with the very light trailer, any faster and it really did bounce a bit if it hit a bump, but the heavier braked trailer for the yacht was fine right up to the legal speed limit.
Jeremy