Yes, there is a little man inside who will unplug the heater if he detects any illegal input below 80MHz.
I'd just try it and see what happens. I can't think of any reason why it wouldn't: people use RF tubes like the ECC88/6DJ8 for audio all the time.
The only thing is that RF tubes are sometimes prone to oscillations because of their good RF performance, so you may need grid stopper resistors that an audio tube in the same circuit could do without. The ECC88 is certainly like this.