|1. I don't think so. I've heard that you technically don't even need to rinse when using soap nuts.
2. Yes, it is. At least as far as I know, I've never seen anything different recomended for front loaders. This is probably because you still need the same amount of cleaning power in any kind of washer. The problem with front loaders and regular detergent is the fact that it sudses too much. This can interfere with the washing action (by cushioning clothing too much as they 'fall' with each turn, the falling against each other and water is what cleans the clothing so a large cloud of suds could interfere with that). It can also get out of the drum and gradually soap off the grease on the inner workings of the washer, possibly eventually causing a breakdown. As long as the detergent is low-sudsing (ie soap nuts, HE detergent or many of the eco-friendly detergents) then you use the same amount in any kind of washer.
3. This is because of the tendancy toward build-up of laundry detergent. Really you don't need any more than half the recomended amount of detergent to wash *anything*, not just diapers. It's just that with clothing, you're unlikely to even notice any build-up whereas with diapers build-up can cause serious and very obvious issues. I never use more than 1/3 - 1/2 of the recomend amount of detergent for anything I wash.
Hope that helps,