I always thought you could justify zombies in the stargate world by blaming a misfunction of the goa'uld (sp?) sarcophagus' healing function. It reanimates the dead, but doesn't restore them completely (mentally and physically)...
Wasn't there a double episode where they did just that? It wasn't a sarcophagus as such, but some other device based on sarcophagus technology. IIRC Dr. Jackson finds it in some forgotten temple in Central America, at which point it begins to zombify the corpses of the local rebel guerillas.
I remember this because they re-ran it on TV recently. Meanwhile the rest of the team were off fighting Anubis' enhanced super-Jaffa. That should help you relate it with whichever season it was from.