Hey Rob,
I do a variety of upright basses (imagine that). One thing that will matter is how that player stands on stage and where because the instrument itself will resonant at some natural frequencies with your mains, whether it is in the monitors or not. This always seems to change with stage/room layout as well. It will be worth ringing out that channel with the bass held in a variety of positions.
As for mics, I have done the 57, actually like a 58 better in the "stuff the tailpiece" rig. Just as good, and easier for changeovers is an AT Pro35 or ATM350 clipped to the F Hole with the mic just off of the wood between the bridge and F Hole. You can also dangle just the mic bud (take it out of the boom) of the Pro 35 inside the bass (For that matter I have dropped a 57 through the F hole and let it sit on the bootom of the inside before. My favorite is a N/D 468 mounted on the bridge (in one of the round holes, if the bridge has oval holes it doesn't work).
The n/d 468 or the pro35 have always given me the best gain before feedback even with the bass on the front line and in the monitors.
I have never done it, but I would like to try a PR31BW on the upright sometime.