Sorry to add to the whine, but you went out on the highway with trailer hubs of unknown (and maybe no) greasing history-- this is gambling with your rig and maybe somebody else's front teeth.
1. It doesn't take that long to jack up each side and spin the wheel, even with a cement block and 2x4, to see if it rumbles. (If so = bad bearing). If it rumbles, stop and check after a mile and see if the hub got hot. If so, stop now.
2. Grease it anyway, even if not replacing old bearings, cannot hurt!
3. Price of new bearings and 2 dollar's worth of grease are really cheap - compared to the alternative.

Now you know- and it was learned the hard way!
Signed, Mr. Ben Thereonce