Cool. That sight did mislabeled them as MK1 Vipers though. Like Thaeris said they only appear to be atmospheric. The real MK1 is just the TOS BSG design. Caprican Viper is indeed a better term.
As for the nose intake, well real planes on Earth used to have them. Specifically the Vietnam era ones like the F4 Phantom and MIG 21s.
I looked more on that site and also found this. Its not cannon but it is an RDM series style viper like fighter design.
Looks quite a bit like the Scorpion, actually, which was canon for TOS. And no, that model is really just a mod of the TOS Viper with a color scheme akin to that of the new series. In all, I do kind of like it.
Personally, I always liked DeSanto's Viper Mk.IV. This isn't actually too far off from the new BSG in some regards as the Mk.VII was a DeSanto design, if my memory serves me correctly. With a bit of a re-design, It could be a pretty neat addition for Diaspora... Though I think it would look good as-is.
Now, the problem with the nose intake on the Caprican Viper is this - it doesn't DO anything. The explanation to the intake on all the space-fairing Vipers was that it was a sensor emplacement, that intake on the Viper is neither a retro engine exhaust or a sensor opening... it's just silly sci-fi engineering.
I thought that nose looked familiar! They stole that nose design from my favorite fighter plane of WWII! That nose is from one of these!
Definately a modified P-40 nose! Seriously!