CL compiles down to the metal in most cases (ABCL being a notable exception). I've written device drivers in CL, realtime code in CL, and many CL implementations even allow you to write in assembler. I've done that too, in order to take advantage of SIMD hardware. The above would be -- problematic -- on top of the JVM.

There also might be an issue of speed, since CL is compiled to the metal. Modern JIT JVMs probably have mostly eliminated CL's speed advantage, but I'd still be surprised if some things in SBCL (arguably the best-optimized CL) didn't run faster than in Clojure.