#1
Is the alnico classic pickups on a epiphone sg-g400 the same as a seymour duncan alnico pro 2 (used by slash)
#2
No.

They're stock Epiphone pickups, and won't be as good as the Duncans. They'll give you a slightly different tone as well, most likely.
#4
You can hear soundclips of the Alnico Pros on the Seymour Duncan websites. The Epiphone pickups aren't brilliant. They're decent enough, but at times can get a bit muddy and generally lack the nice sounds of some other stock pickups.