Using both .gcode and .gbr files in a hybrid 3D printer + circuit etching machine? (RepRap 1.4 with Marlin firmware)
You can use both .gcode and .gbr files one one machine. We do it where I work.

However, when we make prototype circuit boards, we don't print them; we acquire circuit board blanks, and then we either:


Use a diode laser to burn off the top layer of garolite for isolation traces, then do a chemical dip to remove that copper, then another laser burn to expose pads for surface mount components; or
Use a spindle tool to remove the top layer of garolite where needed for pads, as well as mill through the copper layer for isolation traces.


We have not found a printable material that has the conductivity we want in a circuit board.

Source: I work for Hyrel 3D



Note: we don't use Marlin on Arduino, we use in-house firmware on STM32F429 boards.