If you say that stealth under all circumstances does not exist, then that is true - even on earth (our stealth is directional and has all sorts of constraints). However, Atomic Rockets keeps things very general. Perhaps, the most important thing is how you define stealth. If I can remain hidden long enough to reach a position and time to achieve tactical surprise, I would take that. Here are a few things to consider:
1) Directionality does matter. You can suspend a cooling fin reflective and insulated parabolic dish. Attach these with gimbals to an insulated, superconducting tether and you can have a nice directional heat sink. Then, put your space ship behind an actively cooled mushroom cap like structure and you definitely control your signature to one side (at the expense of being even hotter to the other side).
2) Atomic Rockets gets around this by rightly stating that you could not mask any kind of drive signature if you were under active thrust. However, they do state that cold objects launched without drives (say electromagnetically) would be very hard to detect. They limit this to small autonomous attack drones that would light up when they arrive at their attack position. If you consider point 1, then you could expand this to fighters launched from a carrier object of some type.
3) Tactics matter. Consider an orbit using the Sun as a gravitational sling shot to direct an object at its target (one that passes as close as possible to the sun for maximum acceleration). Once this object fires up its drives, it would be visible just to the outside of the Sun, but then would be approaching the target with the Sun at its back. This ship would now have all the resources of a very large 5000K source to help mask its signature.