This has been a problem for decades. There have been episodes of "Gangland" and one or more of the "Somebody Investigates..." programs on it. The Army at one time stated they had at least 1% of the total force affiliated with a gang IIRC. Think about that for a moment. Not a big number but still is approx 14,000 gang bangers in uniform with the current strength. A lot of the problem stems from there being no policy concerning gang membership. You can't be an active member of a gang, but there is no consistant definition of what "Active" means. So Johny Crip joins and recruits but doesn't do any "work" for the gang and he's OK. If he pops for dealing, it's only dealing not gang related activity.
At Lemoore we had started the connections to get a seat on the Gang Task Force. We wouldn't be able to make arrests or do anything off base but did want the intel to see what was happening on base. I left before it really got started.
Yes, they are using military training to become better banger. There have been well planned ambushes on LEOs and other gangs, led by former military members. Some of them are decorated veterans that have two or more combat deployments down range.
The other problem is the ones that join to find access to heavier equipment. I'd put money on some of the heavy weapons found in Mexico came from Mexican and US inventory through MS-13, Norteno, Sureno, or other Hispanic gangs.