Herb sounds like a friendly guy.
Proof — Eminem’s best mate that was shot in a bar a few years back.
The ‘margins’ here may also possibly serve as a metaphor for the barriers of acceptability/skill within the hip hop community at the time.
“Hitting trees” is also a reference to the guerilla tactics employed by the Vietcong during the Vietnamese war. They would hide in trees and spring surprise attacks on the US forces. Royce and Em are like Vietnamese people due to eye shape and the double meaning of tree.