I have carried the ortlieb back-rollers on a Surly front nice-rack. I also have the rear nice-rack and was able to set the clips on the ortliebs up so that they work well front or rear without having to adjust the clips. I think maybe they swap R-L when going F-R...but can't recall for sure...been a while. I'd do this when I needed to use the top of the rear rack for large items, which interfered with the ortliebs.
I have found that the bike still quite manageable even with a lot of weight in the front panniers, provided it is snugly contained. If it "flops" around, then it can be a problem. Side-side inbalance didn't seem to bother me much, so it was better to have one pannier snugly full than two half-filled and floppy.