It's a tricky one, really. Although I agree with this:
I also think it do fit in Energy Weapons since heat is energy.
But yeah, I don't use flamers so I don't care now. I plan on doing it on another playthrough (I do one smoothtalking conventional guns character for House, an unarmed and melee character for Caesar, gonna do an energy weapon character for NCR and an explosives character for Yes Man.)
I'd say just make that Pyromaniac perk use the same skill which the flamers use.
As I have nothing but a minor general knowledge to draw from.
EW's are those that require a power source, circitry, non conventional and non solid projectiles.
They require minimal absorbtion of recoil if any, and are not prone ( or as prone ) to influences such as wind.
They also require containment chambers, housing of dangerous chemicals and electrical / magnetic discharges.
Guns ( you're more in the know here gunny ).
Are weapons that require solid projectiles forced out of a more simple tube due to compressed powder converting into a gas.
They require from simple packed and wadded balls forced out of a smooth bore;
To cartridges with a primer that causes a chain reaction when struck fired from a rifled barrel.
Explosives, from some howitzers needing each component ( Shell, wadding and primer ) loaded individually.
A planted and timed charge, a fire bomb or concusive blast to a simple pin pull and toss.
These require a mixture of skills, timing, discipline, chemistry, mechanics and general judgements in common sense.
So to me flamers could fit in explosives, but just as well in EW's if not more so.
They're a cross skill weapon at best, and instead of being swopped over should have greater perk selection to encourage blending.