the Hellfire Hazard is similar in some ways to the spell Hellfire Ray, but they are not the same thing.
The spell does one thing, which it says, the hazard does another, which it says.
I don't see any particular mystery here.
I had originally intended to do a Hellfire Keneticist for HV.
Thought it would be a simple matter of creating an infusion to take with my fire element....what I found is that Hellfire is rather inconsistently described...both in regards to spells like Hellfire Ray....and some creature abilities that use hellfire....
Best case scenario....do what I did and ask your GM how he/she specifically want's to call it.
The real question to start is, whats the RAW on an Fire/Unholy mix?
If we look for the actual definition of 'Hellfire', its found in "Pathfinder Chronicles: Book of the Damned Vol.1 - Princes of Darkness", page 5:
Hellfire is treated as normal fire, but deals half fire damage and half damage from unholy energy. Damage dealt by hellfire is known as hellfire damage. Evil-aligned creatures and creatures with the evil subtype take no damage from the unholy energy, but good-aligned beings and those with the good subtype take double the normal damage from it. Creatures under the effects of spells like protection from evil are unaffected by this unholy energy, though they may still take fire damage.
By RAW, Hellfire is as above. Emphasis on Unholy Energy mine.
So the question is, is Hellfire Ray Hellfire?
A blast of hellfire blazes from your hands. You must succeed on a ranged touch attack with the ray to deal damage to the target. The ray deals 1d6 points of damage per caster level (maximum 15d6). Half the damage is fire damage, but the other half results directly from unholy power and is therefore not subject to being reduced by resistance to fire-based attacks.
However, this only refers to Unholy Power, not Unholy Energy. I feel its a fairly pedantic case to argue that its not the same thing its referring to. Considering it exists in the same book as the Diabolist, the Trap and the Mechanics themselves (along with many more Hell themed items, artifacts, spells and maps and hierarchies of Hell), I feel the intent is clear that its Hellfire Damage and its meant to use the mechanics from the book.
Other cases of Unholy damage being a thing exist in Asmodeus' Exalted Boon (Hellfire Blast) which deals Fire/Unholy and the Hellfire Bombs Discovery which deal Fire/Unholy.
If you're going to argue that the Lord of Hell's own Boon doesn't grant Hellfire Damage because its worded that "...half the damage from this spell is fire, while the other half is unholy" and its missing the word 'energy' (and instead uses 'damage'), that's just silly.
Its clear from BotD that RAI Fire/Unholy (whether its Unholy Power, Unholy Damage or Unholy Energy) is Hellfire.
I'd even argue that its RAW, going by BotD's mechanics.
tl;dr
RAI 100% meant to be Hellfire damage.
RAW Expect table variation due to the issue of editing changing a word from 'energy' to 'power'.