If you are replacing the rear track arm (looks like a tuning fork on one end), neither end of that arm is used to configure the rear alignment (camber on the inboard end of the lower control arm, and toe on the inboard end of the toe arm, both of those control arms have a rubber bushing on one end and a threaded pin on a ball joint on the other end)
Even if the ball end was totally shot on the rear track arm, (which controls the caster, non-adjustable), in my opinion
it would have a minimal impact on the camber and toe of that rear wheel.
I replaced both of my rear track arms and did not get an alignment, and was ok.
Compromise: take it to a place that offers free alignment checks
Wouldn't hurt to get it checked...