Martin Thompson has basically made a career out of writing Java in the style of embedded C because he found enterprise customers that need the performance of embedded C but, being enterprise, insist on absolutely everything being Java.
calling external code from Java adds latency.
You have to make sure all dependencies don't use GC as well right?
Sure, but I'm assuming that if you're writing such high performance limited scope software like the LMAX disruptor, you have few dependencies (looking at their code, it appears that the disruptor code itself has no external dependencies and uses few of the standard library classes outside of NIO bytebuffers).