I suppose as long as the programmers are ACTUALLY equally skilled it would be fine, but from what I've actually experienced in the real programming world, the C++ programmers are generally all fairly experienced skilled programmers who write effective efficient code. With Java programmers, I have seen quite the opposite, sure there are those experienced skilled programmers who could compete, but a LOT of Java programmers even ones with equal 10-12 years of experience, suck monkey balls at actually writing efficient code. Instead they write code that's JUUUST good enough.
That said I know a number of people in the HFT market and the programming languages are ALL over the place, sure some of them are in Java and some are in C++, but there's not any one dominating language: there's plenty of Python, Scala, Perl, Groovy, and probably every language you can image. I believe Perl is actually still the biggest language because a lot of the financial analysts can actually write it directly and so do stuff that the front end systems don't normally allow.