That's the marketing department's claim, but I'm not so sure, especially against some nations, like Russia and China that have access to the older, long-wave radar systems, so the stealth aircraft can at least be localized.
I suspect, if they can get, or have aircraft aloft, that with I/R detectors, especially from the rear quarter, or rear arcs, they can be found, and shot down.
Stealth jets try to minimize their heat signatures too, but I imagine doing so may be more difficult than covering up their radar signatures.
In fact, they even have to fly slower (sub-sonic), in order to avoid having their wings and other forward fuselage/tail surfaces light up like a Christmas tree from the heat buildup at higher speeds (supersonic).
Some of the newer I/R missiles, and thermal detectors may have quite a good range, so getting them into the ballpark with their L/R radars may be good enough to at least permit them to be engaged, if not actually shot down.
If/when they can be found, WVR weapons may really create a serious danger to them, especially for less capable F-35 stealth jets, and our B-2 bombers.
Sadly, sensors, weapons, and stealth capabilities are classified for us wargamers, but I'll bet our enemies' military personnel have a lot of this info at their fingertips, which makes classifying a lot of it rather moot.