Memnarch can't be a general because of his ability. Also if you choose a colorless general, the entire deck must be colorless.
There are some playgroups that allow him to be played as a general. I haven't put it to mine yet, but if they refuse, I would just swap him with Venser, or remove a card, and play the artifact stealing one legendary.
Metalworker is still banned per the rules here : http://www.dragonhighlander.net/rules.php
I am aware that metal worker is banned in most places. however, in my play group, we have a trust network. We don't really ban cards, but we don't abuse them too crazily either. I am aware that i must switch it out if i am playing with an unfamiliar person.
Funny that Memnarch has been unbanned recently. I doubt it will stay that way, though.