Make Reptilian Domain useful, plz.

[Oroborous]

Magic Fang works on summoned creatures dude, yeah.

It so does not. I just tried.

[Allatum]

Dragons are (generally) incredibly intelligent, powerful magical creatures.

Kobolds, on the other hand, aren't. They are sentient, though, so that throws a kink in the mix.

Imps are sentient, but can be turned/rebuked with alignment domains.

[Zelknolf]

More relevant re: dragons would be, I think, that dragons are their own creature type.

http://www.d20srd.org/srd/typesSubtypes.htm#dragonType

PnP rules ftw.