So CIRCT backend can generate FIRRTL, I think it is certainly possible to use this VLSI flow, and I also think that there is no additional process to be done to use this after generation of FIRRTL from CIRCT MLIR. Is it right?
CIRCT works as a firrtl compiler, compiling it to verilog. There is direct firrtl emission, but it was mainly used for test case reduction. A couple flows pass through firrtl. The better intercept point for hammer is verilog emitted by circt (which is how circt and hammer are usually used togeather).