Depends how hard Namecoin has forked from the core Bitcoin source. Armory grabs its data from the raw binary block files created by the core client. As such it trusts the core client with block verification. This makes porting Armory rather easy.
Assuming Namecoin uses the same transaction signing scheme and EC as Bitcoin, you're left with node port, magic words, fee calculation and dust sweeping/ignoring rules to change. And everything else I possibly overlooked =P
Thanks goatpig, that's good info to have.