One can use optically triggered strobes with an Ikelite housing - it is clear! I have - Timmoranuk does.
The non-OEM housings can go deeper, are just all-around better-made and offer better ergonomics ... things like wheels that spin.
That said - I'm with you ... I'm thinking very seriously about a G11 with an OEM housing, Fantasea add-on wet lenses and optical strobes - INON s-2000s.
I was a very happy G7/G9 owner who currently doesn't have an underwater rig.
I have a G9 with the OEM case, and my gf & I are probably going to buy a G11. We'd like to buy an Ike (or "advanced") housing if possible for it - the main reason we went OEM housing with G9 was because it was our first intermediate camera in the water and are now looking for the next step. OEM housing is fine if:
- you like the small size!
- you're ok with button operation of shutter button (i like the lever of the Ike, but can live with button)
- you're ok with difficult to use wheel spinny thing at back for (mostly) manual focus (i like Ike spinny thing)
One consideration for add-on wet lenses is the size/weight of those add on lenses. I'm not certain i'd want to attach a wide angle (possibly +fisheye bubble) to the OEM case as they are quite big to just add on - but saying that, i have not have this experience first hand!
I AM however in the process of ordering some macro lenses as wet add ons, however no experience at using/handling them underwater. Hopefully it's easy, more reports on that later! 
Cheers!