The aforementioned rappers are challenged to come out with some original concepts, after Voss just called them out on their unoriginality.
In other words, he caught them “red-handed”, which is what “stigmata” is a reference to. Stigmata are bodily marks, often bleeding, on the hands, corresponding with the crucifixion of Jesus.
Example:

Biggie was commonly referred to and seen as a “king”, which leads to this line comparing the majority of today’s “emcees” to paupers.
They are “bumming” (or taking for free without any work put in) other rappers of the past’s styles, similarly to how one would “bum” a cigarette when they’re too broke or cheap to buy their own.

The hip-hop landscape just ain’t the same since the days when Notorious B.I.G. and rappers of his caliber were popular.