No code reason not to mix conductor types.
That said....
If I come across an installation that has mixed conductors I assume someone was using scraps saving a buck etc.
I also generally install copper but would have no problem using an AL EGC with AL circuit conductors.
As far as 'deox' the sales rep is correct, not an NEC requirment. Go ahead and use it if you like. IMO it is of little value.
It comes reinstalled in some crimp connectors my guess it works as both a lube while crushing and keeps water from entering the connector.
[This message has been edited by iwire (edited 05-31-2006).]
