Maybe to some extent? The teams doing proper HFT are all dealing with C++ or hardware. This is true across the industry AFAIK at places like HRT, Citadel Securities, Jump, etc. Some of these might use some Java for things that don't require low latency but those aren't really considered HFT.
All robust HFT shops? What do you mean by robust and how did you come to that (to me) surprising conclusion?
by working there. I would say sure a lot of the platform is written in C, much of the architecture and front end market-making apps are written in C but when it comes to the algo's and tools to spin up new pricing models in a way that is fast, those tools are written in Java.