Yes, the hub would be running at much higher speeds, so that could be a problem. I guess it depends on how much you use the bike if it will be a serious issue or just the inconvenience of replacing the hub later when it slips or wear is detectable. I'm guessing you could get a couple years of frequent use out of one, if the parts inside are steel, and you adjust the bearing cones when necessary. If you use the best high-temp grease like Lucas or something, it should do ok, and maybe it's possible (for someone with wood tools) to add a wooden wheel to the hub similar to your skateboard wheel. That should knock down wear some, and take care of the traction issue (untreated hub shell as roller would be slick).
I planned on using a threaded freewheel adapter and BMX freewheel to go from the dax driveshaft to the 3 speed hub.
On the other hand, if law allows, you could just get a stronger engine and go with the 1.5 roller.