Redneck Revolt is a far-left militia group with over 30 branches nationwide and until recently they offered a downloadable 36 page guerrilla warfare manual on their website that included sections on kidnapping, sabotage, terrorism, and executions.
If the SPLC's track record of clear ideological bias is any indication of how they will operate as a member of YouTube's Trusted Flagger program, then there is zero doubt they will abuse that role. If YouTube is serious about combating extremism on their platform and not just policing conservative voices they should follow the lead of the Federal Bureau of Investigation and Department of Defense and drop the SPLC.
According to a recent article from Wired Magazine, antifa has a new secret weapon, an Elon University Computer Science Professor by the name Megan Squire.
They promote several PDFs that endorse "armed struggle" and even offer a 36 page "Mini-Manual Of The Urban Guerrilla" which pictures left-wing militants using RPGs and outlines tactics for guerrilla warfare including sections on "sabotage", "kidnapping", "executions", "armed propaganda", and "terrorism".