We have ProStride crumb rubber with coarse sand in our outdoor. The sand is washed concrete sand. Regarding the rubber, it shouldn’t be used alone as footing. After a very heavy rainfall we get deep areas of rubber that separates from the sand and floats to the low end of the arena. It is unstable to ride on, and the horses slip. It has to be mixed back in. (Sometimes I will ride before I’ve had a chance to groom the arena which mixes the rubber back in).
We put in a 1:3 rubber to sand ratio totaling 2 inches. It fluffed up to around 2 1/2". I do like the rubber - except for the occasional need to rake it back in after major rain.
Our neighbor has sand footing in his indoor and he has to keep it watered. I don’t think there is any other way to eliminate dust with sand. I think there are additives that help, but I’m not sure of the specifics, and I believe you still have to water it. Even the super expensive footing in the indoor arena at the Kentucky horse park is watered. Of course they have fantastic, large tanks that they drive around and spray with.
You are right - rubber doesn’t really help with dust because it doesn’t hold moisture. I suppose there is less dust, but it doesn’t seem to make a noticeable difference.