Not entirely, but to a degree, yes. I've forgotten what size tank we were talking about, but in tanks over 30g, a skimmer is needed to keep the nutrients in check, and to remove them before they become issues. But, if you tank is under 30g, you'll just need to do water changes of 10-15% once a week to keep those nutrients in check.
As far as mixing salt. You should do this in a seperate container 24hrs before your going to use it. I would not rely on nor use that filter for stirring the salt mix up. Filters are not used as part of the flow equation, as they are inconsistant, and mostly just ruffle the surface. Flow in a FOWLR would be 10x your water volume, and in a Reef tank it would be 20x and up.