Sound vibrations will still be picked up in a vacuum in this case. Vibrations through the rocket body will be transmitted to the camera body (direct contact) which will then be transmitted to the microphone (again, direct contact). According to Wikipedia[1], 90% of the Earth's atmosphere, by mass, is at an altitude of 52,000 ft or lower.

[1] http://en.wikipedia.org/wiki/Atmosphere_of_Earth#Pressure_an...