I'd imagine other HFT companies may also pay for the Azul JVM which goes even further and comes with a kernel module that the JVM coordinates with for memory allocation. The kernel module pre-reserves x% of system memory at the time it is loaded.
Basically one main reason you need to stop the world in common GC's right now (and thus cause pauses) is because if you want to compact memory a GC thread has no idea if other threads reads/writes to an object while moving leading to worst case corrupt/lost writes.
What Azul does is to make the pages in question invalid for reading/writing so any access to them would page-fault and then proceeds to move the objects without worrying about other threads. Since the hardware provides the page-fault "for-free" this protection doesn't cost anything in terms of runtime performance in the common case (compared to the new ZGC made by Oracle that has read-write barriers that steals some mutator performance), worst case if another thread tries to read/write memory that is being moved a specialized page-fault handler detects if this was an page that was in motion and can then do a slower read-write but ONLY in the seldom cases where this occurs (compared to all the time of f.ex. ZGC)