Who handles the tech on all those illegal ships (pirat, smuglar)? Can you fly a ship with warp drive without tech priests or is it OK for a preist to work for scum and pirats?

Typically either 'hereteks'- former members of the Adeptus Mechanicus who have fallen from the True Path of the Omnisiah and been cast out, or enslaved Techpriests (captured or purchased by said pirates) who, despite their predicament, can't bring themselves to betray their beliefs by doing anything other than properly maintain sacred machines.