If you buy water from somewhere, they are likely dumping water as well. Just plumb a RODI in-line to a drain and call it a day. There is a small subset of systems that function appropriately on non-RODI water, and generally these are for very experienced reef aquarist (timfish is the prime ARC example).
The skimmer is going to be pulling out dissolved organic matter, which the cleanup crew would be unlikely to feed on. It has also been my experience that if you overstock cleanup crew, you're going to have a pretty big die off. Additionally, if you don't feed heavily enough, your cleanup crew tends to dwindle in numbers, which leads to a die-off, which leads to algae, which is what you were trying to avoid in the first place. I advocate a small, sustainable cleanup crew of hermits, nassarius, cerith, fighting conchs and limpets to keep nuisance algae under control and to keep the sandbed free of food crumbs.
I don't really see it as an expert/non-expert thing when it comes to skimming. It's an additional tool in the kit that many people choose to use in combination with other methods. It's popular because it's generally simple to operate, and has beneficial side effects (aeration most notably).