The only mechanical way to define what is a fire or water creature is by subtype. Thus, I read it as creatures with the [Fire] subtype. Examples:
FIRE ELEMENTAL, Elemental (Fire, Extraplanar)
RED DRAGON, Dragon (Fire)
RAST, Outsider (Extraplanar, Fire)
THOQQUA, Elemental (Earth, Extraplanar, Fire)
Now this brings us to the Elemental Savant. Does she, or does she not gain the subtype? Looking at the
Elemental Perfection ability, it clearly lists what the Savant gains.
- Type Elemental
- No need to sleep, eat, breathe
- Immune to stunning, critical hits, flanking
- Speed and movement modes
- Natural Attacks
- Special Attacks
- Special Qualities
It often references the chosen subtype which was picked at first level, but nowhere does it say she ever actually GAINS the subtype. Interestingly however, since the Fire Elemental's vulnerability to cold and immunity to fire are listed under its Special Qualities, the Savant gains these even though she never technically gains the [Fire] Subtype, which would give these by default. Of course this also means that the 10th level ability,
Energy Immunity, is redundant. Odd.
(Correction: Earth and Air savants would not normally get the immunities. This gives them acid or electric immunity. Also unlike a fire or water(cold) Savant, neither the Air nor Earth Savant gains the vulnerability which is included in the Special Qualities of the Elementals. Interesting twist.)
Conclusion: Fire domain allows rebuking [Fire] creatures. Savant does not actually have a [Fire] subtype. Fire domain cannot rebuke the Savant.