Rumour has it that the UCA is relatively easy to put out of shape if you clamp it in a vice, Bryan. The theory behind splitting and replacing the ball joint on the car is that it holds everything in place and keeps it where it's meant to be whilst you put the pressure on and do the job.
In all honesty, I'm not sure you'd get enough pressure in a vice to bend the arm, but I suppose better safe than sorry.
It'd be a PITA to hold it well enough to split the bugger if you dropped everything off to do it off the car anyway, IMO. Plus, if you split it and get the ball joint off first, you'll have much better access to the UCA bolts anyway, so I'd do it in that order if I were you.
Sure there'll be differing opinions, but that's mine.

24 hours in a day, 24 beers in a case. Coincidence? I think not…
70 Challenger
MMA/489
NSS/435