I don't know about templates or themes off hand, but you might look in DMG2 for themes (it has a bunch and IIRC is where monster themes originated) and I think either MM2 or MM3 has... some Vecnite monster, maybe enigmas of Vecna or something?
There was a recent Dragon article about Vecna that I think included some new game mechanics (not sure if it had themes or templates or just new feats).
There was a recent Dragon article about Vecna that I think included some new game mechanics (not sure if it had themes or templates or just new feats).
It was in Dragon 395 (January 2011). It's called "Channel Divinity: Vecna" and includes six Vecna-themed feats, two of which enable powers. I think it's more geared to PCs that want to worship Vecna, but you could get some useful ideas for NPCs, I think.