tl;dr: it's exceedingly difficult to hide anything that consumes power in space. the rcs thrusters would either be too weak to achieve the delta v to hit the target, or the friction from the thrust against the nozzle would unstealth the missile. even the radiation from the onboard computer would likely stand out against the cosmic background. a missile like you describe could potentially evade current detection systems, but would almost certainly be detected by any civilization where ship-to-ship space combat is feasible. and not in a handwavy future tech way, but just from extrapolating current tech. I highly recommend checking out that page. it makes for a great read.