Maybe. The L4 people did write one of theirs in C++. L4-style kernrls are among the fastest in existence. Some even fit in the L1 cache of the CPU.

http://www.l4ka.org/projects/pistachio/pistachio-whitepaper....

I can see your point if you're saying compiler use lets them avoid a language they just dont want to use. Which they couldnt if using it for an OS.