In terms of counters I see, other than the duely noted ones...
- Jellicent is immune to Fighting-type and resists Fire-type attacks but fears Wild Charge.
- All Rock, Dragon, or Water and Ground-types (any of the first three types with a combination of Ground-type) resist all of Emboar's Reckless attacks but should be wary of Superpower.
- Physically bulky Water-types like Slowbro and Suicune can switch into Flare Blitz with relative ease but are almost always 2HKO'd by either other Reckless attack. Suicune gets points for being faster and thus being able to Rest off the damage, causing more pain for Emboar while Slowbro heals as it switches out which helps with a mis-predict. Kingdra has x4 resistance to Fire-type and thus can check Emboar quite well. Bulky sets can even prevent Flare Blitz from breaking Substitutes.
- Heatran's ability to nullify Flare Blitz and general bulkiness is useful for checking while Earth Power does considerable damage. Other Flash Fire users are good but weakness to Stealth Rock and Emboar's access to Head Smash limits their switching-in ability.
- Regirock and Gigalith both have huge Defense stats and can take Flare Blitz well while not fearing Wild Charge or Head Smash. Superpower and mix sets with Grass Knot should be watched for. Another Rock-type to mention is Terakion since it also resists Head Smash.
- Water or Ground-types with powerful STAB attacks like Starmie with Surf/Hydro Pump and Excadrill with Earthquake can force Emboar out but must either predict carefully or switch in freely to avoid OHKO's.
On a side note: Fire Blast deals more damage than Scald (180 vs. 160) to things like Gliscor and Grass Knot hits Rock/Ground-types harder than Scald. Scald would be for Camerupt and Magcargo. Also going to mention Adamant CB Flare Blitz KO's standard Jolly Gliscor over 90% of the time with SR down.
@Below: True, added. Kingdra with 252 HP / 68 Defense can put up a Substitute that will never be broken by Adamant Flare Blitz.