What type of airspeed are wind speeds given in?
Wind is measured in true airspeed. That's why whether it's surface wind or a jet stream, subtracting the head/tail wind component from the airplane's TAS yields the ground speed (tailwind being a negative value). And a 25 knots crosswind—the example you give—will create the same crab angle for the same TAS being flown. But since pilots fly using IAS, the crab angle will be smaller the higher the airport.
Cup
Think of a cup anemometer, if the air is lighter (high altitude, high temp), there will be lower resistance and the same wind speed will result in the same rotation:

The remarkable thing is that the calibration does not depend on the air density. Who would have guessed? The cup anemometer responds to wind forces, and those wind forces have a magnitude directly proportional to density. Yet because in a steady state those forces are balanced, density vanishes as a factor.

The same thing applies to the propeller-vane anemometer.
Tube
In tube anemometers (pitot-static on a stick), corrections are applied:

[Due] to differing temperature, elevation or barometric pressure, a correction is required to obtain the actual wind speed. Approximately 1.5% (1.6% above 6,000 feet) should be added to the velocity recorded by a tube anemometer for each 1000 ft (5% for each kilometer) above sea-level.

Ultrasonic
Ultrasonic anemometers are like cup anemometers, density is cancelled out since measurements are taken in multiple directions:

[Scalar] values (temperature, humidity, density) are eliminated and the result comprises wind speed.