Mastering the Koldunic sorcery school of the Way of Fire seems to come with an obvious drawback - seeing fire so often would probably do a lot of unpleasantness to the Cainite performing it. Is there a canon explanation to whether it would?
I'm reading the question as do Way of Fire Koldunic sorcerers have access to any bonuses which directly make resisting Rötschrek easier?
A one-dot power available through the Way of Fire, called Fiery Courage, does this directly:
• Fiery Courage
No vampire can master an element he fears, so this power dims that fear to a mere ember of its former intensity.
System: Once learned, this power is permanent and requires no activation roll or blood. The koldun subtracts his rating in the Way of Fire from the difficulty of Courage rolls to resist Rötschreck from exposure or proximity to flame. This power does not aid in resisting the panic that accompanies sunlight or any other causes apart from actual fire. If this reduces the difficulty of a Courage roll below two, the koldun simply does not succumb to the Red Fear. Koldun never risk Rötschrek from fire and magma they conjure. (Core Rulebook, V20, p. 452)
Otherwise, a high Courage rating is of use in resisting Rötschrek and so a Koldunic sorcerer of this type would probably have (or develop) a high Courage rating (if they're planning to be around fires caused by other means).
Finally, not all fires are created equal. Way of Fire offers a variety of abilities based on hot things, like magma, but little to no effects that directly produce a fire (though they could ignite other things). That helps a lot, since a fire indirectly caused by their use of the Discipline is probably not going to start out as a conflagration.
A lighter-sized flame used to light a cigarette is pretty easy to dismiss, and a bonfire represents some Rötschrek risk but hardly a guaranteed one. Especially with Fiery Courage, a Way of Fire koldun is likely to be well-equipped to deal with any fires of any kind that they might encounter in their work.