Just seen the post was duplicated so copying my reply from the other one:
You can if you have to but you need to make sure it is all properly washed out - I always do a normal nappy wash again after one with stain remover and extra rinses. You'd be better spot treating stains than putting it through the whole wash too.
Really though, I don't see the point. Nappies are there to collect poo and you can pretty much guarantee that if you spend time removing stains from the inside, as soon as you put that nappy back on it will be pooed it! The only time I remove stains is when they're on the outside and haven't shifted after a couple of washes (many stains will fade in time, especially if hung in natural light, anyway) or if I'm selling the nappies.