I know this question was posted some time ago, but just wanted to say I'd suspect few members of this board have ever so much as set foot in Algeria, what with its--somewhat exaggerated--reputation for danger. In any event, good luck if you decide to take the job. If nothing else, it'll be an adventure. I assume--forgive me if I'm wrong--that you'll be working for an oil company and thus will probably be living in a guarded complex. Where Skikda is on the coast, there is little to worry about. Apparently, the road between Annabah and Constantine can be a bit treacherous for a Western European (my father cross Algeria overland along this route a few years ago, and was later told by the DCM at the US Embassy that this was unwise) and the Maghreb should be avoided altogether--but undoubtedly you've been briefed on all of this.
Sorry, but I have no information on diving in Algeria. Please let us know what you find.