I have done, but it very much depends on the reserve and if there is space to do so without blocking paths or breaking any 'stay to the path' requests. Generally speaking, the suitability for hides is inversely proportional to the formalness of the reserve. If it's a car park-shop-colour-coded walk reserve, then you don't have a hope. Whereas a lot of places like Wildlife Trust reserves are little more than unfarmed/developed land and I'd think nothing of sticking up my hide.
One alternative would be a bag-hide, which I reckon you could use without issue are most places (bar blocking paths).
Of course the real problem is that on reserves, you'll have half of your day disturbed by people loudly saying "What's that?" and coming over to investigate or have people think "That must be a good spot to see something interesting" and standing next to your hide!