Most problems with router base offsets can be worked around by finding the desired side that represents a workable offset. Then put a large arrow on the top of the router base with a marking pen that is pointing to the side, and always use this side marked side against your guide. The offset, whatever it is, will always be the same, so you can include it in your calculations. I use a rounded side of my router bases and mark them with the arrow.
When dovetailing, always pointing the arrow at the router jig guarantees that base offset will not be a problem. Even an extreme offset will only serve to create the entire joint shifted slightly from one end to the other, and won't affect the fit of the actual joint itself.
Charley