Apart from Inner Vit, I don't see what makes this combo so unique to Huskar.
Sure your increased magic resist will negate most of the initial damage but purifying flames can't kill allies and will always heal more than the initial burst so in the end any hero will come up winning HP from it.
Add the possible life steal the target might have, a mek by someone and urn (that I don't believe is interrupted during False Promise) and you'll have any hero almost healed to full in the end.
Will Huskar be healed more than anyone else? Sure. Will this combo only work with him? No.
Also from the wiki (regarding False Promise):
It does nothing against his major counters (I believe Frostbite still applies).
Huskar is a hero that benefits from being close to death, but not dead. Oracle's ult is a spell that allows him to stay this way for 6-8 seconds. If there's an axe on the team you just use the ult a little earlier before he is in dunk range. Huskar will almost always get a full heal from the ult due to his Q and lifesteal from helm if he has it.
It's not a complicated combo and it's really fucking effective.