Aluminum drop outs can get chewed up. Some people like to have steel inserts on the drop outs to protect them. Good nuts rotate around without actually grinding up the drop out. I'm sure you have probably seen the nuts I'm talking about, its sort of like a nut with a built in washer with little teeth on it. The teeth dig into the dropout and the nut just presses on the washer. As long as you are not grinding the washer back and forth on the dropout by constantly pulling the chain loose and then retensioning it you should be fine.

So... your drop outs will be fine as long as you treat them well.