Chas,
You must not get out much. I have seen arrangers used in bar/club/upscale restaurant/church/schools. I've seen arrangers in Vegas. Ask Don Mason, Uncle Dave and many others where they use arrangers.
I watched the Paul McCartney New York special the other night. Now I would think Paul could get any players he wanted to perform with him. When he did "Got To Get You Into My Life" I was looking for the brass players. There were none to be found. It was all synth, plastic and artificial. Did it sound good? You bet. I don't know what synth or sampler they were using but it sounded very good.
The point is where do you draw the line? Do all the parts in a live performance have to be performed manually by humans? I'll include drummers in that group.

Is it ok to use electronic substitutes for parts as long as they are manually being played as Paul did?
Is it ok for me to add bass to my band using my pk5 bass pedals or is that too plastic?
Is it ok to use a B3 as long as you use a real bass player?
For most of us it is about the generation of a musical performance (entertainment and total sound)and using whatever tools neccessary to do it.
Tom