The way I understand it, the original gangs can simply be used as is. However: the campaign rules are so simplified, that the experience may vary, as the advancement works so different.
I'm planning to recreate the original Necromunda campaign system for SWA, with slightly different flavors for each faction.
So the campaigns for gangs, guard, orks etc can work 1 on 1. But necrons or nids for example would require a rework of the Outlanders campaign to make sense. And then there are loads of factions inbetween those two extremes.
But I'm pretty sure it can be pulled off. And that way, the original gangs can be integrated seamlessly, which is something I'd like too...