Yeah, it's not technically true these are all identical, but for OP's purposes, they can be treated as such.

I've seen "shoulder blade", "shoulder butt", and "shoulder arm" roasts.
They are slightly different as to the bone in the roast and I prefer the blade for crockpotting.

Same thing.

http://www.porkbeinspired.com/cuts/shoulder-boston-butt/

http://www.chowhound.com/post/pork-shoulder-pork-butt-701828

https://en.wikipedia.org/wiki/Boston_butt

Same.

They are the same.

No are different even though some places will give you shoulder when you ask for butt. Pork butt is fattier.

They're the same thing. Different words, exact same meat.

Somewhere along the way the shoulder acquired the name "Boston Butt." I have no idea why.

What is the difference in the final result if I cook it in the crockpot, or are they basically the same?