The ceiling fans that I've seen have induction motors and their speed control is achieved by switching capacitors in series with the motor. The effect of this is to reduce the motor's running voltage so I would say that, if the dimmer really is suitable for a very inductive load, the answer is yes. But beware of 'dimming' it so far that it won't start.
As per previous posts, regarding "fan speed controller".
It's a different unit to a dimmer switch that you need, they do look very much the same and will have a arrange of speed settings.
It is likely that you will find that the back box that is sunk in to the wall will need replacing for a deeper one. A standard back box for lights is 16mm, because of the additional components on the back of the "fan speed controller" plate. It is very likely that the depth now required will be 35mm.
Thanks for all the replies. I was thinking of a proffessional dimmer rather than a "Knob on the wall" type, But from your replies I will use a proper fan controller.
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